1. Preheat your oven to 375°F. Lightly grease a 9×13-inch baking dish to prevent the casserole from sticking.

2. Heat the olive oil in a skillet over medium heat. Add the chopped onion and minced garlic, and sauté until fragrant. Then, add the ground beef and season with salt, pepper, and Italian seasoning. Cook the beef until it’s browned and crumbled.

3. Start by placing a layer of zucchini slices in the bottom of the prepared baking dish. Spread some of the cooked ground beef mixture over the zucchini, and then add small dollops of ricotta cheese (if using). Repeat these layers until all the ingredients are used up, finishing with a layer of mozzarella and Parmesan cheese on top.

4. Cover the casserole with foil and bake for 20 minutes. Then, remove the foil and continue baking for another 10-15 minutes, or until the cheese is melted, bubbly, and golden brown.

5. Once the casserole is out of the oven, let it cool for a few minutes. Then, garnish it with fresh basil leaves and a sprinkle of red pepper flakes, if desired. Serve hot and enjoy this delicious and comforting meal!