Preheat the oven to 400 degrees F.
On a sheet pan, toss the zucchini and tomatoes with 1 tablespoon olive oil, 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper. Arrange the zucchini on one half of the pan and the tomatoes, cut-side up, on the other side.
Roast the vegetables for 15 minutes, flip over the zucchini and continue roasting for 15 minutes until the zucchini is lightly browned and the tomatoes are wrinkled but still juicy.
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.
For the vinaigrette, whisk the garlic, mustard, 1/2 teaspoon kosher salt, 1/4 teaspoon black pepper, vinegar and 1/4 cup olive oil in a small bowl.
Stir half the vinaigrette into the lentils.
Carefully fold the roasted zucchini and tomatoes, parsley and parmesan into the lentils. Add more vinaigrette as desired.