Cook the rice noodles according to packet directions and rinse with cold water. Set aside.
Fry the curry paste, chilli, garlic and lemongrass in a little vegetable oil until fragrant. Add stock and coconut milk and simmer until reduced to 4 cups.
Adjust the seasoning with fish sauce, chilli sauce and sugar. You can also strain the soup if you like.
In a steamer, reheat the noodles with the bamboo shoots, cucumber and prawns.
Divide the bean sprouts between preheated soup bowls. Ladle in the soup, then garnish with spring onions, coriander, mint and fried shallots. Serve.