1Place yogurt, mint and sugar in blender or food processor. Cover and blend on medium speed, stopping blender occasionally to scrape sides, until leaves are finely chopped.
2Set oven control to broil. Spray broiler-pan rack with cooking spray. Remove fat from lamb. Place lamb on rack in broiler pan. Broil with tops 2 to 3 inches from heat 12 to 14 minutes, turning after 6 minutes, until meat thermometer reads 160° (medium doneness). Serve with sauce.