1. Combine first 3 ingredients in a small bowl.
2. Prepare grill.
3. Trim fat from lamb. Rub lemon halves on both sides of lamb. Coat grill rack with cooking spray, and place on grill over medium-hot coals (350° to 400°). Place lamb on rack; grill, covered, 5 minutes. Turn lamb; spread mint mixture evenly over lamb. Cook 5 additional minutes or to desired degree of doneness. Garnish with mint sprigs, if desired.
Note: In a heart-healthy diet, no more than 30 percent of your calories should come from fat. But not every food you eat has to fall under the 30 percent limit. For instance, when you serve lamb chops (which are naturally higher in fat), be sure to serve a low-fat side dish such as pasta or rice to keep your total fat percentage down at a healthy level.