Fill a large bowl with boiling water then add the noodles and let them sit in the water for 2 minutes until soft. Drain and refresh in cold water.
Heat the groundnut oil in a large wok set over a high heat until. Stirfry the prawns, red onion and chilli for 1 minute then drain the noodles and add to the wok. Toss and stir frequently for 2-3 minutes until heated through. Remove from the heat and add the chopped coriander and the soy sauce.
Toss and stir well before serving.