Preheat oven to 180°C. Using the tip of a sharp knife, cut a cross-hatch pattern all over the lamb skin. Combine fish and sweet chilli sauces, chopped mint and 1 tbs oil in a bowl. Place lamb on a rack set in a roasting pan and brush all over with marinade. Fill pan with 2cm hot water, then cover pan with foil. Roast for 11/2 hours, then remove foil and roast for a further 45 mins. Cover loosely with foil and set aside to rest for 15 mins. Carve and serve with vegetables of your choice and Chilli Mint Sauce.