Drain out the liquid from the walnut pickle and heat it in a saucepan over medium flame along with the green onion.
Let the mixture come to a boil and simmer for another 10-15 minutes till it reduces.
Add pickled walnuts, soy sauce, mustard seed, chill powder, ginger, cayenne pepper and the anchovy to another saucepan over a medium flame and bring this mixture to a boil.
Simmer it for about half an hour and pour in the reduction mixing thoroughly.
Simmer the sauce for 15 more minutes and turn off the flame.
Cool the sauce completely and then refrigerate for few days.
After refrigeration for a couple of days, strain the sauce and serve it with broiled fish.