Zucchini Squash Casserole

4.67 from 6 votes

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You don’t need a baking dish for this easy zucchini squash casserole. That’s because it starts in a skillet on the stove, and then you bake it in the oven. This is a lighter casserole recipe and is not overly cheesy. It’s topped with toasted breadcrumbs and grated Parmesan. The zucchini and squash are seasoned with garlic and oregano. It bakes in 30 minutes.

For another summer vegetable casserole, try this Balsamic Zucchini Tomato Bake.

Spooning out squash casserole from the skillet onto a small plate.

Why You’ll Love This Recipe

This is a healthy casserole that features vegetables more than cheese. Many casseroles are rich because they have lots of melty cheese. Here the Parmesan in the topping is light, and it’s more about layering in flavor. 

The casserole goes from stovetop to oven to table all in a skillet. By starting the casserole with sautéing onions and then adding garlic and spices, you have the chance to really develop the flavors. On their own, zucchini and squash are pretty mild. You need to add other ingredients to enhance them and make them more exciting.

If you have a lot of zucchini and squash during peak season, this is an easy way to use it. Just like tomatoes, you can find yourself overloaded with summer squash, and this casserole is a wonderful and simple way to cook it.

The Ingredients

Ingredients including squash, zucchini, onions, garlic, olive oil, parmesan and spices.

This is what you need:

  • Zucchini & yellow squash: The best zucchini and squash will have smooth skin and feel firm. Both are categorized as summer squash. I like to make this recipe with equal amounts of each for a balance of green and yellow colors, but it doesn’t matter as long as you have 1-1/2 pounds total for the casserole.
  • Garlic: The recipe calls for 3 cloves minced. You use fresh garlic instead of garlic powder because it sautés with the onions.
  • Onions: This is where the skillet comes in. When you sauté the onions, they become the base for the garlic and seasonings, which the squash needs. A white onion or yellow onion is fine.
  • Panko breadcrumbs are Japanese breadcrumbs that are very crisp and crunchy. Their texture is a nice contrast with soft baked vegetables in any casserole.
  • Parmesan: I combine Parmesan cheese with the breadcrumbs for the topping. 
  • Olive oil: For the best taste, I use a good extra virgin olive oil especially because this recipe doesn’t have that many ingredients.
  • Oregano, red pepper flakes, salt and black pepper go into the skillet with the minced garlic. Overall they give the casserole Italian/Mediterranean flavor.
  • Parsley: For fresh herbs, I finish the baked casserole with chopped parsley. You can also use torn basil leaves, fresh thyme or minced chives. 

How To Make This Zucchini Squash Casserole Recipe

Preheat the oven to 350 degrees F.

1. Salt the zucchini and squash to remove the moisture. The easiest way to do this is to put the sliced veggies into a colander and toss them with kosher salt. Then let them sit for 10 minutes. You will see drops of water appear on the zucchini and squash. Pat them dry with a towel.

2. Prep the breadcrumb topping. In a small bowl, stir the panko breadcrumbs, Parmesan and olive oil.

Zucchini and squash in a colander. Breadcrumbs, parmesan and olive oil stirred together in a small bowl.

3. Warm the oil in a large skillet over medium high heat.

4. Sauté the onions. Give them 3-4 minutes to start to soften.

Olive oil warming in the skillet. Onions sautéing.

5. Add the minced garlic and seasonings. They will become fragrant in a minute or less.

6. Stir in the squash and zucchini. The skillet will be very full, so do slow strokes with a wood spoon. The goal is to have the onions and garlic distributed evenly throughout the zucchini and squash.

Garlic and onions sautéing and then zucchini and squash stirred into the skillet.

7. Sprinkle on the breadcrumbs.

8. Bake the casserole until it is golden brown top and the vegetables are tender. It will be ready in 25-30 minutes. Garnish with chopped parsley.

Casserole in a skillet before and after is it baked.


This vegetable casserole is great as a side dish with vegetarian main dishes such as Tomato Basil Pasta, Pesto Gnocchi or Cherry Tomato Eggplant Pasta. It is also good with chicken, salmon and other proteins. Think about dishes with vegetables that go with zucchini and squash such as tomatoes, corn and eggplant.

Storage & Leftovers

You can store leftovers in the refrigerator in an airtight container up to 3 days. It is best to put them in a wide shallow dish, so you are not covering up all the breadcrumbs. Or they won’t get crispy again when you reheat them. 

Warm leftovers on a parchment paper or foil-lined sheet pan in a 350-degree F oven. They will reheat better if you spread them out. The zucchini and squash rounds can be overlapping like they were in the skillet, but don’t stack them on top of each other.

Zucchini and yellow squash casserole baked in a skillet.

Recipe Tips

Don’t skip salting the squash and zucchini. It only takes 10 minutes, and if you don’t do it, you will end up with soft, mushy vegetables, especially at the bottom of the skillet.

Cut the zucchini and squash the same thickness. This will help the casserole cook evenly.

Use small to medium squash and zucchini. During summer, it is common to see gigantic zucchini. If the diameter of the slices is too wide, they will be hard to stir into the onions and garlic in the skillet.

Always use an ovenproof skillet. This makes the recipe easy to go from sautéing on the stove to baking in the oven.

Recipe FAQs

How do you keep zucchini from getting soggy in the oven? 

Toss cut zucchini, whether it’s sliced or diced, with kosher salt in a colander. Wait 10 minutes and then dry the excess moisture with a towel. By removing this extra water content, you will avoid soggy zucchini.

Can you use all zucchini or all squash in this casserole recipe?

Yes, yellow squash and zucchini are interchangeable. Use what you have in your kitchen, it does not have to be an exact 50-50 split between the vegetables.

How do you make this casserole gluten free?

All you have to do is use gluten-free breadcrumbs.

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Zucchini Squash Skillet Casserole

4.67 from 6 votes
Prep: 10 minutes
Cook: 35 minutes
Total: 45 minutes
Servings: 6
This easy zucchini squash casserole starts with sautéing onions, garlic and oregano in a skillet. Then the vegetables are topped with panko breadcrumbs and Parmesan before they bake in the oven.


  • 1-1/2 pounds small to medium zucchini and yellow squash sliced 1/4-inch thick
  • 1 teaspoon kosher salt
  • 1/3 cup panko breadcrumbs
  • 1/3 cup grated Parmesan
  • 2 teaspoons + 2 tablespoons olive oil
  • 1/2 cup chopped onions
  • 3 garlic cloves minced
  • 1/2 teaspoon oregano
  • 1/4 teaspoon red pepper flakes
  • 1/4 teaspoon black pepper
  • Chopped parsley for serving


  • Preheat the oven to 350 degrees F.
  • Toss the zucchini and squash with 1/2 teaspoon kosher salt in a colander. Let them sit for 10 minutes. Pat off the excess moisture with a towel.
  • Stir the breadcrumbs, parmesan and 2 teaspoons olive oil in a small bowl.
  • Heat 2 tablespoons olive oil in a 10-inch ovenproof skillet over medium high heat. Sauté the onions until they start to soften, about 3-4 minutes. 
  • Stir in the garlic, oregano, red pepper flakes, 1/2 teaspoon salt and pepper cook until fragrant, about 30 seconds to 1 minute.
  • Stir the zucchini and squash into the garlic and onions, so everything is well mixed together. Make sure the the zucchini and squash are spread evenly in the skillet.
  • Sprinkle the breadcrumb-parmesan mixture on top.
  • Bake the casserole for 25-30 minutes until it is lightly browned and the zucchini and squash are tender.



As long as the total weight is 1-1/2 pounds, you can use more zucchini or more summer squash than the other. It does not have to be an equal mix. You can also use all of one type.
To make the recipe gluten free, use gluten-free breadcrumbs.
Store leftovers in the fridge in an airtight container up to 3 days. Put them in a wide shallow dish so you are not covering up all the breadcrumbs. Or they will be soft and won’t get crispy when you reheat them. 
Warm leftovers on a parchment paper or foil-lined sheet pan in a 350-degree F oven. The zucchini and squash can be overlapping like they were in the skillet, but don’t pile them on top of each other.


Calories: 108kcal | Carbohydrates: 6g | Protein: 3g | Fat: 8g | Saturated Fat: 2g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 5g | Cholesterol: 5mg | Sodium: 321mg | Potassium: 146mg | Fiber: 1g | Sugar: 2g | Vitamin A: 152IU | Vitamin C: 8mg | Calcium: 71mg | Iron: 1mg

Nutrition information is automatically calculated, so should only be used as an approximation.

Additional Info

Course: Side Dishes
Cuisine: Mediterranean
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Hi, I'm Paige.

Welcome to Last Ingredient where you will find simple seasonal recipes with plenty of fruits and vegetables, all for the home cook.

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