PREHEAT THE BROILER. Peel the prawns and discard the shells. Using a small sharp knife, split the prawns partially and remove the fine digestive cord. Pat the prawns dry with paper towels. Mix the marinade and combine with the prawns and let sit for 10 minutes. Prepare the sauce ingredients and mix together and set aside. Lay the prawns on a baking tray big enough to fit under the broiler. Or alternatively, you could cook them on the barbecue, weather permitting. Cook the prawns 3 minutes on one side, turn and cook for 2 minutes on the other. Turn onto a serving platter and serve with the sauce.