Spray a baking sheet in cooking spray. Pre-heat oven to 400°F.
Place frozen meatballs, or homemade meatballs, in a large saucepan. Add your pasta sauce. Fold the meatballs in the sauce. Heat on low heat, stirring occasionally, until they are thoroughly heated.
You can fill a roll with as many meatballs (usually between 4-5 and 6 depending on the size of your roll). Add more pasta sauce to your pot. Place the filled sandwiches on a baking sheet. Sprinkle shredded mozzarella cheese on each sandwich.
Bake until cheese melts, is hot and bubbly.