1. In a bowl, combine ground beef, breadcrumbs, egg, garlic, onion powder, salt, and pepper. Mix well and form into 12-15 meatballs.
2. Heat olive oil in a skillet over medium heat and cook the meatballs until browned on all sides. Remove and set aside.
3. In the same skillet, sauté onions until soft, about 5 minutes. Stir in flour and cook for 1 minute.
4. Add beef broth and Worcestershire sauce, whisking to create a smooth gravy. Simmer for 2-3 minutes.
5. Return the meatballs to the skillet and spoon the gravy over them. Cover and simmer for 10 minutes until fully cooked.
6. Sprinkle mozzarella and Parmesan cheese over the meatballs. Cover and cook for another 2-3 minutes until the cheese is melted and bubbly.
7. Garnish with parsley and serve hot.