In a small bowl combine well the bread crumbs, the oil, the thyme, the cumin, and the garlic. Season the lamb with salt and pepper and rub the fat side with the mustard. Pat the crumb mixture evenly over the mustard and arrange the lamb, crumb side up, in a roasting pan. Roast the lamb in the middle of a preheated 475°F. oven for 15 minutes, or until a meat thermometer registers 130° to 135° for medium-rare meat, transfer it carefully to a cutting board, and let it stand, uncovered, for 10 minutes. Cut the lamb between the ribs and divide it between 2 plates.