Marinate and Fry Fish: Marinate fish pieces with turmeric powder, chilli powder, lime juice, and salt. Fry in hot oil on both sides and set aside.
Prepare Onion Tomato Paste: In the same oil, sauté onions and tomatoes with salt. Blend into a fine paste.
Cook Spices: Heat oil, add mustard seeds, cumin seeds, red chillies, chopped ginger, garlic, and curry leaves. Fry till they splutter.
Combine and Cook: Add onion-tomato paste, chilli powder, coriander powder, and tamarind juice. Cook by adding water until oil oozes out.
Finalize Curry: Add fried fish pieces, cook briefly. Finish with coriander leaves, cover and cook for 2 minutes. Turn off the flame.