In a small saucepan, combine juice, sugars and salt; bring to a boil, stirring to dissolve sugar. Cook, uncovered, 10-15 minutes or until mixture reaches a glaze consistency. Remove from heat; stir in mustard and orange zest., Sprinkle chicken with lemon pepper. On a lightly greased grill rack, grill chicken, covered, over medium heat 6-8 minutes on each side or until a thermometer reads 170°, brushing occasionally with some of the sauce during the last 5 minutes. Serve with remaining sauce.