Soak the rice noodles in warm water for 20 minutes; drain.
Heat 3 tablespoons oil in a wok or large heavy frypan over medium high heat. Saute noodles for 1 minute. Transfer to serving dish and keep warm. Add remaining 2 tablespoons oil to frypan and saute onion, garlic, ginger, prawns and pork for 1 minute. Stir in bok choy, oyster sauce and chicken stock. Season with chilli flakes. Cover and cook for 1 minute, or until bok choy is wilted. Spoon over noodles and garnish with spring onion.