Sauce (nuoc mam cham)
Whisk together the fish sauce, water, lime juice and sugar. Stir in the garlic and chilli.
Place the rice vermicelli in a bowl, pour boiling water over the top and leave to absorb for approx. 6 mins., pour away the liquid, rinse in cold water, drain.
Puree the lemongrass, shallots, garlic and 2 tsp of oil in a food processor or using a mortar and pestle, mix in the meat. Heat the remainder of the oil in a frying pan. Stir fry the meat in batches for approx. 2 mins. Pour in the fish sauce and cook for approx. 1 min.
Serve the lettuce, vegetables and herbs in bowls. Top with the rice vermicelli and meat, pour the sauce over the top. Top with the peanuts and fried onions.