Add the oil to a large heavy based frying pan, and warm a little, then add the paste and cook for a minute. Then stir in the ginger, scallions and peppers and coat in the paste. Pour in the coconut milk, and boil for 2 minutes, stirring from time to time.
Season the fish and add to the mixture in the pan and gently simmer for 5 minutes until the fish is beginning to flake. Add the chopped herbs and lime juice.