Preheat your oven to 375°F (190°C). Sprinkle the eggplant slices with salt and let them sit for about 30 minutes to draw out excess moisture. Pat dry with paper towels.

In a large skillet, heat a tablespoon of olive oil over medium heat. Add the chopped onion and garlic, sauté until soft. Add the ground beef or turkey, breaking it apart as it cooks until browned. Drain excess fat if necessary.

Stir in the tomato sauce, diced tomatoes, Italian seasoning, salt, and pepper. Let the mixture simmer for about 10 minutes to blend the flavors.

Lightly grease a 9×13-inch baking dish. Start by layering half of the eggplant slices at the bottom. Spread half of the meat mixture over the eggplant. Dollop half of the ricotta cheese and sprinkle with a third of the mozzarella.

Add the remaining eggplant slices, followed by the rest of the meat mixture, and dot with the remaining ricotta cheese. Finally, top with the remaining mozzarella cheese.

Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes. Then, remove the foil and bake for an additional 15-20 minutes, or until the cheese is bubbly and golden brown.

Allow the casserole to rest for about 10 minutes before cutting and serving.