Preheat oven to 375

Add 1 Tbsp. olive oil to a sauce pan and add the sliced onion. Cook for about 10 minutes or until onion is browned and just beginning to caramelize

Add the minced garlic to the onion and cook for another minute until garlic is fragrant

Spray a deep casserole dish with cooking spray and place the onion mixture on bottom, spreading to cover

Alternate placing the zucchini, squash and tomato in the dish, keeping the slices upright against the edges of the dish

Drizzle with 1 Tbsp olive oil and top with a dusting of dried basil leaves

Cover with foil and place in oven for 40 minutes

Remove from oven and top with parmesan cheese

Return to oven, uncovered for 30 minutes

Let rest a few minutes and serve.