For the dressing, pound the chilli and sugar to a paste using a pestle and mortar. Add the fish sauce and lime juice, continue to pound until well mixed.
Run the lettuce under cold water. Remove and discard the two outer leaves. Peel the other leaves away one at a time until you get to the smaller ones - set these aside. Put the outer leaves in a big food bag in the fridge for another time.
Shred the mango and the carrot into sticks using a food processor, or a sharp knife. Mix the mango, carrot, grapefruit, radishes and spring onions together with the herbs, beansprouts and peanuts. Mix in the dressing and leave to sit for 2 mins. Serve in a bowl next to the pile of reserved lettuce leaves. Spoon the salad into the lettuce leaves and eat with your hands.