Combine the onion, lemongrass, garlic, lime juice, sesame oil, tea oil and chilli together and pour over the prawns. Set aside to marinate for 1 - 2 hours.
Soak the noodles in boiling water until they are soft, Drain thoroughly and set aside to cool.
Heat the coconut oil in wok until hot and stir fry the prawns and capsicum for approx 3 minutes until cooked.
Toss the prawns through the noodles with the fresh herbs and green beans, fish sauce and lime juice. Sprinkle the roasted peanuts over the top and serve.