Mix together the mango chutney, paprika and lemon or lime juice in a small bowl.
Heat half the oil in a frying pan or sauté pan and fry the prawns for about 3 minutes, turning once, until pink, then immediately drain them from the pan.
Add the potatoes to the pan with the remaining oil and fry very gently for about 10 minutes, turning frequently, until the potatoes are golden and cooked through. Add the garlic and cook for a further 1 minute.
Add the tomatoes and bring to the boil. Reduce the heat and cook gently until the sauce turns pulpy. Stir in the creamed coconut and mango mixture and cook gently until the coconut has dissolved into the sauce.
Stir in the prawns for a few seconds to heat through. Check the seasoning and serve scattered with mustard and cress or chives.