1. Take any firm white fish or rohu or katla and cut into pieces. Marinate with 1 tsp. turmeric powder and salt and keep aside for 15 minutes.

2. Heat 2 tbsp. mustard oil in a skillet. Cook fish fillets till they are golden brown on both sides or for about 2 minutes each side.

3. To make curry, heat mustard oil. Add mustard seeds & kalonji. Now add  onion paste, ginger garlic paste and green chillies.

4. Saute for about 5-8 minutes till browned.  It should be almost cooked.

5. Add tomato paste along with spices -- cayenne, coriander powder, turmeric powder, garam masala (if using) and salt.

6. Cook for about 5 minutes on low flame to assimilate everything.

7. Add a cup of water and fried fish pieces. Cover and cook for about 3-4 minutes. Garnish with lemon juice and serve hot.