METHOD 

1. Heat Oil In A Pan Add Mustard Seeds Stir Heat Until They Begin To Splutter. Add Garlic And Ginger And Stir For A Half Minute Add Green Chilies. Add Onions And Sauté Until Brown. 
    
2. Add All Spices And Tomatoes. Fry For 2-3 Minutes.  Add Fish Salt And Vinegar. Cover And Simmer For A Few Minutes Till The Fish Is Almost Tender.
    
3. Then Add Coconut Milk. Stir Only Once Or Twice And Very Gently To Make Sure That The Fillets Do Not Break.
    
4. Adjust The Seasoning. Garnish With Coriander Leaves.