Heat coconut milk and chicken stock in a stockpot over medium heat for 3 minutes. Do not allow to boil.
Add the lime leaves, galangal, chillies and lemongrass.
Stir in the chicken or seafood and mushrooms. Cook until the soup just begins to boil. Turn off heat. Add the lime juice and fish sauce. Mix well. Remove and serve hot, garnished with spring onions and coriander leaves.