Cover the fish pieces with salt and 1/2 teaspoon of turmeric powder.
Heat a pan with 2 tablespoons of oil and fry the fish pieces. Set the fried fishes aside.
In the same pan with the oil, fry the onion slices. Add the garlic, coriander, dry red chilli and cumin pastes. Now sprinkle 1/2 teaspoon of the remaining turmeric powder, and add green chillies and 1/2 cup of water. Cook until the water dries up and the oil starts to simmer and float on top.
Now add 2 more cups of water to the curry mixture.
When the water starts to bubble, add the fried fish pieces.
Turn the heat down to a medium level, and cook with lid on for 15 minutes.