2. Step
Combine ground beef, panko, onion, basil, egg, Italian seasoning, salt and crushed red pepper in a large bowl; gently mix with your hands (do not overmix). Form the mixture into 16 (about 1 1/2-inch) meatballs, nestling the meatballs into the pasta mixture as you work. Pour the remaining marinara sauce over the casserole and top with cheese.