Stir together dressing and buttermilk, blending well.
Layer a 3-quart glass bowl with half each of lettuce and next 6 ingredients; top with half of dressing. Repeat layers with remaining ingredients and dressing. Cover and chill 2 hours. Prep: 25 min., Chill: 2 hrs.
For testing purposes only, we used T. Marzetti's Roasted Garlic Dressing.