Toast the seeds and dried red chilli, then grind in a pestle and mortar, or spice grinder. Heat a little oil in a pan and cook the onion with a big pinch of salt until soft and golden. Add the ginger, garlic, turmeric and ground spices and fry for 1 minute. Add the coconut, tamarind and green chillies and simmer for 5 minutes.
Add the fish and cook for 3-4 minutes until just cooked. Serve with rice.