Bring 4 cups (1L) of water with the stock paste to the boil. Also, bring a separate pan of water to the boil to cook the noodles in; cook noodles according to directions on pack.
Meanwhile, combine mince, spring onion, chilli, coriander, ginger and soy sauce.
Roll level tablespoons of mixture into balls. Heat oil in a large non-stick frying pan. Cook meatballs until browned all over and cooked through. Remove from pan; drain on absorbent paper and add to stock.
Add bok choy and mushrooms to stock and cook for 2 minutes.
Divide the shiitake mushrooms, bok choy, noodles and meat balls in the soup bowls, ladle over hot soup.