Cook the egg in boiling water for 5-6 minutes for soft boiled or longer for hard boiled. Plunge into cold water and when cool enough to handle, peel the egg and set aside.
Put the vegetable stock in a pan with the sweet chilli sauce, peanut butter and soy sauce and whisk together.
Bring up to a simmer while you slice the mushrooms and cut the bok choy into wedges. Add both to the pan, along with the noodles. Cook until the noodles are just soft, around 2-3 minutes.
To serve, ladle the soup and noodles into a large bowl, cut the egg in half and add to the bowl.
