In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add the finely chopped onion and minced garlic. Sauté for about 3-4 minutes, or until the onions are soft and translucent.
Introduce the ground turkey or chicken to the skillet. Break it apart as it cooks and continue to cook for approximately 5-7 minutes, until fully browned. Season with salt, pepper, oregano, basil, and optional red pepper flakes.
In a large mixing bowl, combine the sliced zucchini rounds with a sprinkle of salt. Allow them to sit for about 10 minutes, then pat them dry with a paper towel.
In a rectangular casserole dish, spread half of the pizza sauce evenly over the bottom.
Layer half of the cooked ground meat mixture over the sauce, followed by half of the zucchini slices, black olives, diced bell peppers, and one-third of the mozzarella cheese. Repeat with the remaining ingredients, finishing with the last bit of pizza sauce and mozzarella cheese on top.
Sprinkle the grated Parmesan cheese over the top layer of mozzarella.
Cover the casserole dish tightly with aluminum foil and bake for 25 minutes. Remove the foil and continue baking for an additional 15-20 minutes, until the cheese is bubbly and golden brown.
Allow the casserole to cool for about 5 minutes before slicing.
Notes
For added flavor, garnish with fresh basil leaves and a drizzle of pizza sauce before serving.