1Heat coals or gas grill for direct heat. Place 1 chicken breast half, 2 sliced tomatoes and 1 sliced zucchini on one side of four 18x12-inch sheets of heavy-duty aluminum foil. Spoon 2 tablespoons pesto over chicken mixture on each sheet.
2Fold foil over chicken and vegetables so edges meet. Seal edges, making tight 1/2-inch fold; fold again. Allow space on sides for circulation and expansion.
3Cover and grill packets 4 to 5 inches from medium heat 20 to 25 minutes or until juice of chicken is no longer pink when centers of thickest pieces are cut. Place packets on plates. Cut large X across top of packet; fold back foil.