In a large mixing bowl combine cubed bread with grated onion/garlic, Worcestershire sauce & milk. Mash with a fork for a couple of minutes until the bread absorbs the moisture. Add in egg, parmesan, parsley, oregano, salt and pepper. Stir/mash again with a fork until evenly combined.
Add in pork and beef and use your hand to combine. Mix until the bread mix has evenly incorporated with the meat. Try not to overwork the meat or the meatballs will come out dry. Use a 1 tbsp measuring spoon to scoop out chunks of meat and spread out on a baking tray. Once you've scooped out all the meat, roll each chunks into balls.
Spray with oil then pop under the grill on high heat and broil until browned all over, shaking/turning a couple of times during.
Meanwhile, in a large pan over medium heat add a drizzle of oil along with your diced onion. Fry until the onion starts to turn golden, then add in garlic and fry for 1-2mins longer. Pour in tomato passata then add basil, oregano, chilli flakes, salt, sugar and pepper. Give it a good stir then turn down the heat to a simmer.
Add in the meatballs and some of the char/juices along with them (for extra flavour). Coat the meatballs then gently simmer for around 20mins until the sauce gets nice and thick. This is not only important to reduce the sauce but also to marry the flavours together.
Spread a couple of spoonfuls of the sauce down the centre of your subs, then add in 4 meatballs per sub. Top with mozzarella then sprinkle with parmesan. Pop on a baking tray and grill/broil on medium heat until the cheese goes gooey and golden.
Sprinkle over torn basil or some small basil leaves (optional) then serve up and enjoy!