Method
1.	Heat the oil in a large pan.  Add the mustard seeds and as soon as they begin
	to pop, add the onions, green chilli, ginger strips and curry leaves.  Stir and
	cook over a medium heat for 5-7 minutes or until the onions are brown.
2.	Add the chilli powder and turmeric, mix well and sauté for another 2 minutes.
3.	Stir in the water and bring the mixture to the boil.  Lower the heat and cook for
	5 minutes.
4.	Next add the prawns and mangoes then raise the heat to medium and
	continue cooking for another 5 minutes, stirring occasionally.
5.	Lower the heat.  Add the coconut milk and simmer for another 5 minutes,
	stirring constantly until the sauce thickens and the prawns are well cooked.
6.	Add salt to taste and serve hot.