PREPARATION:

1. Prepare grill for direct cooking.
2. Combine mustard and garlic in small bowl; spread half of mixture over one side of lamb. Sprinkle with half of chopped rosemary; pat into mustard mixture. Turn lamb over; repeat with remaining mustard mixture and rosemary. Insert meat thermometer into center of thickest part of lamb.
3. Place lamb on grid. Grill, covered, over medium coals 35 to 40 minutes or until thermometer registers 160°F for medium or until desired doneness is reached, turning every 10 minutes.
4. Meanwhile, soak rosemary sprigs in water, if desired. Place rosemary sprigs directly on coals during last 10 minutes of grilling.
5. Transfer lamb to carving board; tent with foil. Let stand 10 minutes before carving into thin slices. Serve with mint jelly, if desired.