Pour ½ cup Garlic Basil Italian Dressing over chicken breasts and marinate in refrigerator 30 minutes up to 3 hours. Preheat oven to 375°F and place chicken breast in shallow roasting pan. Roast 30 minutes or until chicken is fully cooked.
Meanwhile, place potatoes in a large saucepot and add cover with water. Bring to a boil over high heat and boil 15 minutes or until potatoes are tender. Drain off water and rinse briefly in cold water. Toss potatoes with ½ cup Dressing, celery and mayonnaise. Refrigerate covered tochill.
Arrange tomatoes, mozzarella cheese and avocado on 4 small plates. Drizzle with remaining dressing.