Layered Salad with Roasted Garlic Dressing

2 large heads of garlic
2 tsp extra-virgin olive oil
1 cup mayonnaise
1/2 cup buttermilk
1/3 cup coarsley chopped basil
2 large heads of Romaine lettuce, cut into bite-sized pieces (about 16 cups)
1 large fresh fennel bulb, halved, cored, thinly sliced (about 2 cups)
1 15-15 1/2 oz can garbanzo beans (chickpeas), rinsed, drained
1/2 cup pitted coarsely chopped kalamata olives
12 oz grape tomatoes, halved
2 medium zucchini, trimmed, cut into 1/8 inch rounds (about 2 cups)

Preperation:

Preheat oven to 400F. Cut off top 1/2 inch from galic heads. Place garlic heads in foli, cut sides up. drizzle each with 1 tsp olive oil. Enclose garlic heads in foil. Roast until soft, about 1 hour. Unwrap;cool. Squeeze galic from skins into blender. Add mayonnaise and buttermilk; puree. Add basil; blend until chopped. Season with salt and pepper.
Place lettuce in bottom of large glass bowl. Top with fennel slices, then garbonzo beans, olives and tomatoes. Spread zucchini salad, covering. Spread dressing over zucchini. Cover; chill at least 1 hour.

Can be made 8 hours ahead. Just before serving, toss salad.