Preheat the oven to 350°F (175°C).
In a large mixing bowl, combine ground beef, breadcrumbs, Parmesan cheese, parsley, egg, garlic, salt, and black pepper. Mix until just combined, being careful not to overwork the meat.
Shape the mixture into meatballs, about 1 inch in diameter. You should get approximately 20 meatballs.
Heat a skillet over medium heat and add a little oil. Brown the meatballs in batches on all sides. They don’t need to be cooked through as they will finish cooking in the oven.
In a baking dish, spread the cooked pasta evenly. Pour the marinara sauce over the pasta and mix gently to combine.
Place the browned meatballs on top of the pasta and sauce mixture. Sprinkle Italian seasoning and red pepper flakes over the dish.
Top with shredded mozzarella and additional Parmesan cheese.
Cover the baking dish with aluminum foil and bake for 30 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Let sit for a few minutes before serving.