Cook the noodles according to the packet instructions or until al dente. Drain and rinse with cold water to stop them from cooking.
Heat the oil in a wok over a medium-high heat and fry the onion, garlic and fresh chilli for 1-2 minutes. Add the chilli oil and the prawns and stir fry for a further 1-2 minutes, turning the prawns. Once the prawns have started to turn pink, add the beansprouts and cook for 1-2 minutes.
Add the noodles and the soy sauce then continue to stir-fry until everything is hot and the prawns are cooked through.
Turn off the heat and drizzle over the sesame oil.
To serve sprinkle over the sesame seeds and coriander.