Brush chicken on both sides with some of the 1 tablespoon balsamic vinegar; set aside. For a charcoal grill, place chicken on the rack of an uncovered grill directly over medium coals. Grill for 12 to 15 minutes or until chicken is no longer pink (170 degrees F), turning once and brushing with the remainder of the 1 tablespoon vinegar halfway through grilling. (For a gas grill, preheat grill. Reduce heat to medium. Place chicken on the grill rack over heat. Cover and grill as above.) Cut each chicken breast half into 1/2-inch-thick slices.

Meanwhile, wrap pita bread rounds in foil. Place on the grill rack directly over medium coals. Grill about 8 minutes or until bread is warm, turning once halfway through grilling.

For sauce: In a small bowl, use a fork to stir together mayonnaise, goat cheese, milk, and the 1 teaspoon vinegar. Stir in green onion.

To assemble, arrange spinach, pear slices, and chicken in pita bread halves. Spoon about 1 tablespoon sauce into each pita.

Preheat broiler. Brush chicken with vinegar as directed. Preheat broiler. Place chicken breast halves on the ungreased rack of a broiler pan. Broil chicken 4 to 5 inches from the heat for 12 to 15 minutes or until chicken is no longer pink (170 degrees F), turning once and brushing with the remainder of the 1 tablespoon balsamic vinegar halfway through broiling. Heat pitas according to package directions. Continue as directed.