Heat a large frying pan until very hot then add the minced pork or beef. Cook briskly, stirring with a spoon until the fat starts to render out and the meat begins to crisp and darken. Transfer the meat to a sieve and drain off the fat.
Heat the vegetable oil in the same pan and briefly fry the mushrooms until tender and golden in patches. Add the chilli, garlic and spring onions and fry for another minute then return the meat to the pan. Add the fish sauce to taste, lime juice and sugar and fry until the meat is cooked through.
Spoon a little of the hot meat mixture into the centre of a lettuce leaf, wrap up and eat immediately.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.