GRILL DIRECTIONS: Heat grill. Cut four 18x12-inch pieces of heavy-duty foil. Place onion, zucchini, summer squash and tomatoes on each piece of foil. Sprinkle with salt and pepper; drizzle each with 1 tablespoon oil. Sprinkle with cheese. Wrap each packet securely with double-fold seals, allowing room for heat expansion.
When ready to grill, brush chicken with 2 teaspoons oil; sprinkle with seasoned salt. Place chicken and veggie packets, seam side up, on gas grill over medium heat or on charcoal grill 4 to 6 inches from medium coals. Cook chicken 12 to 15 minutes or until chicken is fork-tender and juices run clear, turning once. Cook veggie packets 15 to 20 minutes or until vegetables are crisp-tender, rearranging packets several times during cooking. Open packets carefully to allow hot steam to escape.