Position rack in center of oven and preheat to 230ºC . Season lamb with salt and pepper. Brush lamb with 1 tablespoon mustard. In small bowl, combine remaining 2 tablespoons mustard with remaining ingredients. Press crumb mixture over top of lamb.
Arrange lamb crumb side up in roasting pan. Roast 10 minutes. Reduce heat to 200ºC . and roast until thermometer inserted into center of meaty part registers 60ºC . for medium rare, about 15 minutes longer. Let lamb stand 10 minutes. Carve lamb, cutting between ribs, and serve.