Heat oven to 375. Coat round baking dish with cooking nonstick spray. Heat 1 T of olive oil in large skillet. Add onions and saute until translucent. Add garlic and cook another minute. Spread onion mixture on the bottom of the pan. Slice the potatoes, squash and tomatoes in 1/4 inch slices. Layer alternately in the dish on top of the onions, fitting them tightly into a spiral making only one layer. Season with salt and pepper and thyme. Drizzle remaining oil over the top.

Cover with foil and bake for 40 minutes or until potatoes are tender. Uncover and sprinkle the Parmesan cheese on top and bake for another 30 minutes or until browned.