Gather meatballs, marinara sauce, sub rolls, mozzarella or provolone cheese, and butter or olive oil
Cook the meatballs until fully heated through if using pre-cooked meatballs
Simmer the meatballs in marinara sauce until coated and hot
Split the sub rolls lengthwise
Optional: toast the rolls lightly
Spoon meatballs and sauce into each roll
Top with sliced or shredded cheese
Optional: broil until the cheese melts
Serve immediately