Rub the lamb leg with Teriyaki or soya sauce, olive oil and parsley. Stud with ginger root and allow to stand.
Preheat oven to 1800 C oven and place lamb on a roasting rack and tray with 250 ml of hot water. Baste occasionally during cooking with pan juices and cook for 1½ hours or until an internal temperature of 600 C is reached. Steam your favourite vegetables separately.
Rest lamb after cooking for 15 minutes under foil before carving. Add brown stock to pan juice to make sauce, add mustard if desired. Season lamb to taste with black pepper and salt, then serve.
Carve roast into 1.5 to 2 cm slices by carving across the grain and serve 2 to 3 slices per portion.