Finely puree the prawns, fish and the remaining ingredients with the coconut milk. Add the lemongrass and all the ingredients up to and including the Kaffir lime leaves to the fish mixture and briefly puree again. With wet hands, shape the mixture into 12 evenly-sized balls and lightly press flat. Heat the oil in a frying pan and fry the fishcakes all over, over a medium heat, for approx. 8 mins. Serve warm or cold together with the mango, lime & chilli sauce.