Giant Mozzarella Stuffed Meatballs

Name: Giant Mozzarella Stuffed Meatballs
Ingredients: 1 1/2 pounds ground beef; 1 small onion, grated; 2 cloves garlic, minced/grated; 1/4 cup parmigiano reggiano (parmesan cheese), grated; 1/2 teaspoon ground fennel; 1/2 teaspoon salt; 1/2 teaspoon pepper; 1 teaspoon oregano (or Italian herb blend/seasoning); 1 pinch red pepper flakes (to taste); 1 tablespoon parsley, chopped; 1 large egg; 1/2 cup bread crumbs (gluten-free for gluten-free); 6 ounces mozzarella, cut into 12 (about 1 inch) cubes