Heat the oil in a saucepan. Add the onion, ginger and garlic and fry until pale golden. Stir in the curry paste, then mix in the coconut milk, chicken stock and fish sauce.
Bring to the boil, stir in the chicken, cover and simmer for 15 minutes. Stir in the vegetables and cook for 2 minutes, then add the noodles and the coriander, torn into pieces, and heat until the noodles are piping hot.
Spoon into bowls and serve with chopsticks or a spoon and fork.