Put all the ingredients for the spice paste into a food processor and process to a rough paste.
Warm a griddle pan and cook the chicken breasts for 5-7 minutes on each side until cooked. Remove from the pan and slice into thick strips.
Heat a wok or deep sided pan over a moderate heat then tip in the paste and fry for a minute, stirring so it doesn’t burn. Add the chicken, followed by the coconut milk then bring to the boil. Shake in a little fish sauce.
Drop the noodles into boiling water then drain and divide between four bowls. Ladle in the chicken and its sauce and serve.