Begin by preheating your oven to 350’F.
Make the tomato sauce. In a cast iron skillet saute a large yellow onion and garlic, add that to a bowl with a large can of crushed tomatoes, basil, oregano, salt, and pepper. Immersion blend until mostly smooth. Some chunkiness is okay!
Spread the tomato sauce in a 1/2 thick layer on the bottom of a deep pan.
Thinly slice eggplant, tomatoes, yellow squash, and green zucchini. Layer on top of each other in neat rows.
Bake for 30 minutes covered. Uncover and bake for another 15 minutes.