Toast the coriander seeds, cumin and dried chillis in a dry frying-pan for about a minute. Crush in a pestle and mortar, then mix in the ginger, garlic, turmeric and 1 tsp salt.

Heat the oil in a wok or frying pan over a medium heat, then add the onion and fry until soft and golden. Add the sliced chillies and cook for another minute.

Add the coconut milk, sugar, tamarind or lemon juice and bring to just under the boil. Immediately turn down the heat and simmer for about five minutes, until the sauce has thickened slightly. Taste for seasoning.

Season the fish with salt, then add it with the prawns to the sauce and simmer gently for about four minutes until the fish is cooked through and the prawns are bright pink. Check again for seasoning. Serve with basmati rice and garnish with herbs.