Heat the oil in a large frying pan over a medium heat and fry the shallot, lemongrass, garlic and chilli for 3 mins until fragrant. Add the pork mince and stir-fry for about 10 mins more until the pork is cooked through and browned. Add the fish sauce, sugar and lime juice, and cook for a couple more minutes until the pork is coated in the mixture. To freeze, leave to cool completely, then transfer to a freezer bag, seal and lay flat in the freezer (so the mince stays in a thin layer). Will keep for up to two months. Defrost in the fridge overnight before using. Reheat in a dry frying pan over a low heat until piping hot.

Divide the pork mince between the lettuce leaves and garnish with the spring onions, carrots and herbs, then serve.