Preheat your oven to 375°F (190°C) and prepare a baking sheet with cooking spray or aluminum foil. Set aside.

In a large mixing bowl, combine the ground beef, Italian seasoned breadcrumbs, egg, salt, Italian seasoning, garlic powder, and ground black pepper. Mix until well combined.

Using 1 Tablespoon of the meat mixture, form a ball and flatten it in your palm. Place a cube of mozzarella cheese in the center, then wrap the meat around the cheese, forming a ball. Make sure the cheese is completely enclosed.

Repeat the process with the remaining meat mixture and mozzarella cubes, making approximately 20 meatballs.

Place the meatballs on the prepared baking sheet, evenly spaced apart.

Bake in the preheated oven for about 20-25 minutes, or until the meatballs are cooked through and the cheese is melted and gooey. Turn halfway through cooking time.

While the meatballs are baking, heat the marinara sauce in a saucepan over medium heat until warmed through.

Serve the mozzarella stuffed meatballs hot, with the marinara sauce spooned over the top or on the side for dipping.