Gather meatballs, marinara sauce, sandwich rolls, and shredded mozzarella or provolone
Heat the meatballs in a saucepan with marinara sauce until hot
Slice the sandwich rolls lengthwise without cutting all the way through
Toast the rolls if desired
Spoon meatballs and sauce into each roll
Top with cheese
Place the sandwiches under a broiler or in an oven until the cheese melts
Serve immediately