Using a sharp knife, cut open the prawns right to the tip of the tail. Open up the prawns fully into a "butterfly". Mix the prawns with the lime zest, lime juice and chilli pepper, marinate for approx. 10 mins.
Heat the oil in a wok or a wide-bottomed frying pan. Fry the prawns in batches for approx. 2 mins. per batch, remove from the pan and reduce the heat.
Heat the oil in the same pan, sauté the onion and curry paste. Add the carrots, papaya and Kaffir lime leaves, cook briefly. Pour in the coconut milk and bring to the boil. Reduce the heat, simmer for approx. 5 mins., season with salt. Add the prawns and heat gently.