Fry the onion until golden in the ghee or groundnut (peanut) oil. Add the coconut, garlic and spices, and cook for a further 5 minutes. Stir in the water and yoghurt, and cook until the onion is soft. Add the prawns and lemon juice or tamarind liquid, and continue cooking for a further 5–8 minutes. Serve immediately on a bed of steamed or boiled rice.