Preheat the oven and cook the meatballs in the oven as per the pack instructions (usually around 25 minutes) while you make the sauce.

Heat the oil in a large pan on a medium heat and then add the onion and garlic. Fry on a medium heat for 3-4 minutes until soft (do not burn). 

Add the whole and tinned tomatoes to the pan (NOTE: you might want to remove the 'stalky' bits before adding the whole tomatoes if you don't like these!). Fill each tin with a dash of water (approx 1/8 of the tin) and slosh around to catch any leftover juices. Add this to the pan. 

Add the basil, oregano, chilli flakes and salt to the pan, stir and bring to the boil. Turn down slightly to a simmer, and leave for 20 minutes, stirring occasionally with a wooden spoon. Each time you stir, use the spoon to 'smush' the whole tomatoes down. Once the meatballs are cooked, add them to the sauce and stir well.

Slice your bread rolls in half lengthways (so you can open them up but they are still joined at the bottom) and place on a separate baking tray. Place 2 slices of cheese on each roll and bake in the oven for 1-2 minutes until the cheese has just melted.

Remove the rolls from the oven, then spoon 3 meatballs and a good helping of sauce into each sub (if you're doing this for 3 people then you can put 4 meatballs in per person). Sprinkle with parmesan cheese and serve.