Arrange bell peppers, cut-side up, in a baking dish; season with salt. Pour enough water into dish to be 1/4-inch depth.
Heat a large skillet over medium-high heat. Cook and stir beef in the hot skillet until browned and crumbly, about 4-5 minutes; drain and discard grease. Add tomato sauce, tomato paste, salt, oregano, garlic powder, and black pepper to ground beef; bring to a boil. Reduce heat and simmer until flavors blend, about 10-15 minutes.
Fill each bell pepper with a heaping tablespoon cottage cheese; top with a layer of mozzarella cheese, a layer of Cheddar cheese, and meat sauce. Sprinkle each pepper with more mozzarella cheese and Cheddar cheese.
Bake in the preheated oven until peppers are tender and cheeses are melted, about 50 minutes.