Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9 inch deep dish pie plate.
Whisk together eggs and oil in a bowl with salt and pepper. Stir in baking powder and baking mix until moistened. Gently fold in zucchini, summer squash, and onion. Pour into prepared pie plate, and arrange sliced tomato over top. Sprinkle with Parmesan cheese to taste.
Bake in preheated oven until puffed and golden brown, about 35 minutes.