Cook the noodles according to the instructions on the packet. Drain, rinse well and set aside.
Pickle the cucumber in equal quantities of rice vinegar and sugar for 5 minutes, drain and set aside.
Mix the egg with 3 tablespoons water. Spray a wok or large frying pan with oil and, when it is quite hot, make a thin omelette with the egg mixture. Roll it up, leave to cool and cut into thin strips.
Combine the shallots, garlic, ginger and ground coriander in a large bowl. Add the peppers, chillies, fish sauce, prawns and noodles and mix in, using 2 spoons to lift and stir, until they are thoroughly combined. Add the soy sauce and salt to taste.
Transfer to a serving dish and serve with the omelette strips, pickled cucumber, coriander leaves, peanuts and spring onions, and with prawn crackers on the side.