Preheat the oven to 200°C. Remove any excess fat from the neck and body cavities of the duck. Rinse the duck thoroughly & pat dry with kitchen towel. Pierce the skin of the duck all over (at roughly 1 inch intervals) with a skewer. Rub salt and pepper onto the skin of the duck. Position duck on a rack over a deep roasting tin to catch the fat, which will drip off as it roasts. Pour 750ml boiling water over the duck and into the roasting tray. Roast the duck for around 90 minutes or until no fat remains and the skin is crispy and brown. Prick the duck to check and if the juices run clear it is cooked. Put roasted duck in a steamer over rapidly boiling water and steam for 1 hour. If preferred, duck can be steamed the night before. Make a cut lengthwise down breast of duck with a sharp cleaver but do not cut through. Heat oil for deep-frying in a wok until hot. Fry duck, turning over occasionally, for 15 ᆨ minutes until skin is crisp and golden brown. Cut duck into serving-sized pieces and arrange neatly on a dish. Drain oil from wok, leaving a little to cook sauce. Heat oil and add combined sauce ingredients. Stir until sauce is thick. Spoon over duck and sprinkle with roasted sesame seeds. Serve hot, garnished with coriander leaves and tomatoes.