Heat grill. Cook couscous in water as directed on package. In medium bowl, combine all remaining ingredients except chicken; mix well.
Cut four 18x12-inch pieces of heavy-duty foil. Place 1 chicken breast half in center of each piece of foil. Top each with 1/4 of vegetable mixture. Wrap each packet securely using double-fold seals, allowing room for heat expansion.
When ready to grill, place packets, seam side up, on gas grill over medium-high heat or on charcoal grill 4 to 6 inches from medium-high coals. Cook 13 to 15 minutes or until chicken is fork-tender and juices run clear. Open packets carefully to allow steam to escape. Serve chicken and vegetables over couscous.