Preheat oven to 400 degrees F. Lightly coat a round pie pan with nonstick cooking spray. Set aside.
In a medium pan, heat olive oil. Once hot, add chopped onion and garlic, cooking until soft and fragrant, 5-7 minutes. Spread the onion and garlic mixture on the bottom of pan. Evenly arrange the sliced vegetables on top, alternating as you go. Once you get all the way around, continue layering to fill the middle until no open space remains.
Drizzle all over with 1 Tablespoon olive oil and sprinkle with Italian seasoning, salt and pepper. Cover with aluminum foil and bake covered for 30 minutes.
Remove aluminum foil and sprinkle with mozzarella and Parmesan. Return to oven and bake uncovered for an additional 15 minutes, or until cheese is golden brown.