Put the pork mince, the beef mince, garlic, chilli flakes (if using), egg and breadcrumbs in a large bowl. Season, then combine well with your hands. Form into 16 meatballs and set aside on a baking tray lined with baking parchment.

For the sauce, heat the olive oil in a deep frying pan over a medium heat and cook the garlic and gochujang (if using) for 1 min, stirring. Pour in the tomatoes and half a can of water. Bring to the boil, reduce the heat to a simmer and bubble uncovered for 15-20 mins. Season with salt and pepper.

Heat 2 tbsp olive oil in a second frying pan over a medium heat until shimmering. Carefully add the meatballs to the pan and cook on all sides for 3-4 mins until golden. Transfer the meatballs to the tomato sauce and cook for 7-8 mins until the meatballs are cooked through. Heat the grill to high.

Fill each split submarine roll with four meatballs and plenty of sauce, then put on a tray, sprinkle over the mozzarella and grill for 4-5 mins until golden and bubbling. Sprinkle over the sesame seeds and spring onion, if using. Serve with fries and slaw, if you like.