Peel and finely chop the ginger. Finely slice the spring onions.
Put the sesame oil in a large saucepan or wok over a medium heat. Add the ginger and spring onions and cook for one minute until they start to become fragrant.
Add 100ml cold water, the fish sauce and the soy sauce, then stir in the coconut milk. Bring to a simmer.
Add the noodles. Allow them to heat through and break up.
When the noodles are ready, stir in the sliced cucumber and chopped coriander. Eat immediately.