Put the stock and 60ml water into a wok or frying pan and bring to the boil. Add the sesame oil and ginger, reduce the heat and simmer for 2 minutes. Stir in the miso paste.
Add the spring onions, mushrooms and pork and simmer for 3-4 minutes. Stir in the noodles and simmer for 1 minute, then add the spinach and coriander and cook for a further minute so the spinach is just wilted.
Ladle into warmed bowls, garnish with the extra coriander and sliced fresh red chilli, if liked.