Preheat oven to 400˚F. In a saute pan, heat a small amount of oil over medium heat. Add onion & garlic & cook for 5 minutes or until softened.
Grease a 9x9 square baking dish & spread the softened onions across the bottom.
Thinly slice the yellow squash, zucchini squash, red potato, & roma tomatoes by hand or using a mandoline. Layer alternately in the pan on top of the onions.
Salt & pepper the tops of the vegetables & then drizzle the Italian dressing evenly over the vegetables.
Cover with foil & bake for 30 minutes. Remove from oven, take off the foil & sprinkle the parmesan cheese over the top. Bake uncovered for an additional 15-20 minutes or until the cheese browns.