Put the ginger, garlic and lemon grass in a saucepan with about ½ pt / 280 ml. water. Bring to the boil, and simmer for a few minutes. Lower the heat, drop in the pork, and poach for 3–5 minutes. Remove with a slotted spoon, drain, and put to one side. Poach the prawns in the same stock until just firm, opaque and pink. Remove and drain them. When cool enough to handle, peel and de-vein the prawns, and chop into two or three pieces.
Line a platter or salad bowl with lettuce or radicchio leaves. The cucumber can be prepared either as long shreds taken off with a potato peeler, 2–3 in / 5–7.5 cm strips or by quartering lengthways. Place in a sieve, sprinkle with salt, and leave to drain for 20–30 minutes. Peel the thick skin from the pomelo, and then remove the tough thin skin from each segment. Break the segments up into small pieces, and put in a bowl with the carrot, bean sprouts, onion, ginger and lemon grass. Rinse and dry the cucumber, and add to the vegetables. Mix together the lime juice, sugar and fish sauce, and stir in the shredded herbs and chillies. Add water if necessary to thin down the mixture. Stir this into the salad, and add the pork and prawns. Let the mixture stand for a while so the flavours can develop, and then spoon into the salad bowl. Scatter the crushed peanuts on top, and garnish with more herbs before serving.