Clean and cut the fish, marinate with salt and a pinch of turmeric. Pan fry the fish, keep aside.
Soak 2 tbsp black mustard seeds in 1/4 cup water for 15-20 minutes. Blend it to a fine paste.
In a wide bottomed skillet, heat 1 tbsp oil and add 1 tsp black mustard seeds. When it starts to splutter, add green chillies, dry mango pieces /amchoor and turmeric powder. Fry for a min and add 2 cups of water.
When water starts to boil, add mustard seed paste, salt and cook for 2 mins.
Add the fish, cover and cook on medium heat.
When the fish is almost cooked, add mango ginger paste and let simmer for another minute.