Preheat Your Oven: Set your oven to 375°F (190°C). Lightly coat a baking dish with cooking spray or olive oil.
Prepare The Meat Mixture: In a mixing bowl, combine the ground beef, half of the shredded mozzarella cheese, Parmesan, egg, chopped onion, garlic powder, Italian seasoning, salt, and pepper. Mix everything together thoroughly with your hands.
Tip: Don’t overmix the meat mixture—it can make the meatballs tough. Mix just until the ingredients come together.
Form The Meatballs: Scoop out portions of the meat mixture using a cookie scoop or your hands, then roll them into evenly sized balls. Place the meatballs in the prepared baking dish, leaving a little space between each one.
Add Sauce & Cheese: Pour the pasta sauce evenly over the meatballs, covering them completely. Sprinkle the remaining shredded mozzarella cheese on top for that gooey, melty finish.
Bake Until Bubbly: Pop the casserole dish into the preheated oven and bake for 25–30 minutes, or until the meatballs are cooked through and the cheese is golden and bubbly.
Garnish & Serve: Once done, let the casserole rest for 5 minutes before serving. Garnish with fresh parsley if desired, and enjoy!