1. In a small bowl stir together yogurt and ranch salad dressing.
2. In a medium bowl combine chicken, broccoli, carrot, and, if desired, nuts. Pour yogurt mixture over chicken; toss to coat. Spoon chicken mixture into pita halves. Wrap tightly in plastic wrap and chill up to 24 hours. Pack sandwiches in insulated containers with ice packs. Makes 4 sandwiches.