1. Clean the fish properly.
2. Marinate the fish with salt and turmeric powder and keep aside.
3. Make a fine paste with ginger and tomato.
4. In a small bowl, add the turmeric powder, cumin powder, coriander powder and sugar and make a smooth paste with little water. keep aside.
5. Place a non-stick frying pan over medium heat, add 3 tbsp oil.
6. Once the oil becomes hot and changes colour, shallow fry the fish and keep aside.
7. In the same pan add the tempering ingredients.
8. Add the ginger and tomato paste and cook for 15 secs.
9. Add the spice mixture and add salt to it and cook for a few seconds.
10. Pour in ½ cup of warm water and add the fish and cook in low to medium flame till the fish is well cooked.
11. Once the fish has cooked, add the remaining mustard oil and green chillies and cover with a lid so that all the flavours are nicely incorporated.
12. Serve with hot steamed rice.