1Preheat oven to 375 degrees F (190 degrees C). Lightly butter a 9x9-inch pan.
2In a large bowl, combine Cheddar, Parmesan, oregano, basil, and garlic. Season with salt and pepper, and set aside.
3Arrange half of the zucchini slices in the pan. Sprinkle 1/4 of the cheese and herb mixture on top. Arrange half of the tomatoes, and top with another 1/4 of the cheese mixture. Repeat layers.
4Melt butter in a skillet over medium heat. Stir in onions, and cook until soft and translucent. Stir in breadcrumbs; cook until they have absorbed the butter. Sprinkle on top of casserole.
5Cover loosely with foil, and bake in a preheated oven for 25 minutes. Remove foil, and bake until the top is crusty and the vegetables are tender, about 20 minutes.
Footnotes
Tip
Aluminum foil can be used to keep food moist, cook it evenly, and make clean-up easier.