Blend the miso paste with a dash of the stock in a saucepan to make a thick, smooth paste. Add a little more stock to thin the paste and then pour in the remainder. Add the ginger, garlic and chilli and bring almost to the boil.
Reduce the heat to a gentle simmer and stir in the noodles, stirring until they have softened into the stock – about 5 minutes.
Add the spring onions, peas, runner beans, mirin, sugar and vinegar and stir well.
Cook gently for 1–2 minutes until the vegetables have softened slightly. Ladle into bowls and serve immediately.