Preheat the oven to 400 degrees F.

Cut the leaves off the cauliflower and trim the rough end off the stem. Cut the cauliflower into 1/2-inch thick slices.

Toss the cauliflower and onions with 1 tablespoon olive oil, 1 teaspoon kosher salt and 1/2 teaspoon black pepper and spread over a sheet pan. Roast for 15 minutes. Then flip the cauliflower to the other side to continue roasting until browned, about 10-15 minutes. Transfer the cauliflower to a cutting board to roughly chop.

While the cauliflower is roasting, place the lentils and 1 teaspoon salt in a medium saucepan and cover with water by 1 inch. Bring to a boil and then reduce to a low simmer with the lid partially on the saucepan. Cook for 15-20 minutes until the lentils are just tender. Taste them to check their doneness after 15 minutes. Once the lentils are ready, pour them into a strainer and rinse with cold water. Transfer the lentils to a large bowl.

Stir the cauliflower, onions, olives, pistachios and parsley into the lentils.

To make the vinaigrette, whisk together the garlic, lemon juice, olive oil, salt and pepper in a small bowl.

Pour the vinaigrette into the salad and stir to combine.