Combine the stock, garlic, ginger, soy sauce, chilies and shitake mushrooms in a soup pot. Gently simmer 5 minutes. Stir in miso until it dissolves. Add the snow peas, prawns and tofu and return to a simmer, do not boil. Ladle soup into bowls, sprinkle with green onions and serve.
Note: Miso can be found in the dairy section. Cooked, peeled prawns are sold in the seafood department.