Combine ground beef, breadcrumbs, minced garlic, Italian seasoning, salt, pepper, and a beaten egg in a large bowl.
Cut mozzarella cheese into small cubes.
Take a portion of the meat mixture, flatten it slightly, place a cheese cube in the center, and carefully seal the meat around it.
Repeat until all the meatballs are prepared.
Heat olive oil in a skillet and brown the meatballs on all sides.
Transfer them to a baking dish and bake at 190°C (375°F) for 15–20 minutes, or until fully cooked.
Serve hot with marinara sauce and garnish with grated Parmesan cheese and fresh parsley.