My favorite toppings for turkey meatball subs is good old-fashioned melted mozzarella cheese. Even melted provolone is tasty. u003cbr/u003eu003cbr/u003eBesides cheese, you can use basic sub toppings like lettuce, onions, and even banana peppers are delicious. u003cbr/u003eu003cbr/u003eOr sauteed onions and peppers (cooked or raw) taste great!