In a small pan, stir together the meatballs and marinara sauce over medium heat.
Split the sub rolls in half and place on a baking sheet, cut-side up. Spread lightly with butter and sprinkle garlic salt over the top. Bake 3 minutes, or until lightly toasted.
On the bottom half of each sub, place 4 meatballs and sprinkle with mozzarella cheese. Top with the top half and bake another 3 to 5 minutes, or until the cheese is melted.
Enjoy while hot!
Notes
Storage: I wouldn't recommend storing whole meatball subs as they tend to get soggy, but you can store the meatballs and sauce separately and assemble later. imply place the meatballs and sauce in airtight containers and store in the fridge up to five days.Reheat: Combine the meatballs and marinara and reheat on the stove or in the microwave.