1. Make a paste of the mustard with about 6 tablespoons of water.
2. Heat oil in a non-stick pan and fry the mustard paste and turmeric powder for about 5 minutes on low heat.
3. Add 3 cups of warm water and mix well.
4. Bring to boil.
5. Add the fish, green chillies and salt and cook on medium heat till the fish is cooked and the gravy thickens a bit.

Recipe courtesy: Anglo-Indian Recipes