Heat the oil in a heavy-based saucepan or karahi over a medium heat. When hot, add the mustard
seeds and fry for 30 seconds, then stir in the onion and garlic and fry gently for about 10 minutes
until softened and lightly golden.
Add the curry leaves, chilli powder, coriander and turmeric and fry for two minutes, then stir in the
tomatoes, tamarind liquid, green chillies and salt and simmer for about 10 minutes until rich and
reduced.
Add the fish, cook for a further five minutes or until just cooked through, and serve with plain rice.