Place chicken steaks in large shallow glass baking dish. Pour 1/2 cup dressing over chicken. Cover; marinate in refrigerator 30 minutes. Combine mayonnaise, basil and garlic; mix well. Refrigerate.Drain chicken discarding marinade. Grill chicken and vegetables over medium coal 10 to 12 minutes or until chicken and vegetables are tender, turning and brushing frequently with remaining dressing. Cut vegetables into strips. For each serving, spread two slices foccacia with mayonnaise fill with chicken and vegetables.