Soak the rice noodles in a bowl of warm water for about 20 minutes. Drain them in a colander or sieve.
Cut the chicken into thin slices.
In a large pot or wok, bring the chicken stock to a simmer, add the fish sauce, pepper, sugar and chilli and cook for 5 minutes. Then add the noodles and cook for another 3 minutes. Finally add the chicken, spring onions and beansprouts and sim