Preheat your oven to 375°F (190°C).
Spread half of the marinara sauce evenly on the bottom of a 9x13-inch baking dish.
In a large mixing bowl, combine the cottage cheese, shredded mozzarella, grated Parmesan, egg, dried oregano, garlic powder, salt, and black pepper. Mix until well combined.
Spoon the cottage cheese mixture over the marinara sauce in the baking dish. Spread it out evenly. Pour the remaining marinara sauce on top and arrange the sliced bell peppers, black olives, and mushrooms on top. Sprinkle fresh basil if using.
Bake for 30-35 minutes, or until the top is bubbly and golden. Let it cool for 5-10 minutes before slicing.