Spinach Garlic Meatballs Stuffed with Mozzarella

Ingredients:

1 pound ground beef or a mix of beef and pork 

1 cup fresh spinach, chopped

4 cloves garlic, minced

1/4 cup plain breadcrumbs

1 large egg

1/4 cup grated Parmesan cheese

1 teaspoon salt

1/2 teaspoon black pepper