To begin, roughly grind together the spices for the spice mix in a pestle and mortar or electric grinder and set aside. Mix together the lemon, turmeric, chilli powder, tamarind paste and sea salt, then rub this mixture over the fish fillets and leave to marinate for about an hour

Heat the oil in a wok over a medium heat and fry the onions until browned and cooked through. Remove with a slotted spoon and drain on kitchen paper. Set aside

Using the same oil, pop in the nigella seeds, cumin seeds and dried red chilli. When they start to splutter, add the ginger and garlic and cook until lightly browned, do not let the ginger and garlic burn. Add the lime pickle and green chillis and cook for a further minute

Stir in the yoghurt and cook on a medium heat until the oil separates from the curry sauce and the yoghurt is cooked through. Add a splash of water if the curry is getting too thick. Add the fish and onions, cover and cook on a low heat until the fish is nearly cooked through

Sprinkle over the ground spice mix, cover and cook for a final 2-3 minutes, or until the fish is cooked though. When ready to serve, return the onions to the wok and reheat

Serve the curry with fragrant Basmati rice or naan bread