Preheat the oven to 200°C.
Heat the leftover meatballs and sauce in the microwave or on the hob.
Slice the sub rolls in half, leaving one side “hinged”, ready to fill.
Divide the meatballs and sauce between the two rolls, then sprinkle over the grated cheese.
Place on a baking tray and cook for 8-10 minutes, until the cheese has melted.
Remove from the oven and enjoy!