Preheat oven to 425°. Stir together lemon zest and 1 Tbsp. olive oil in a large bowl. Add bread cubes, and toss to coat. Arrange in a single layer on a baking sheet. Bake 5 minutes or until crisp. Let cool completely (about 15 minutes).
Meanwhile, combine butter lettuce and next 4 ingredients in a large bowl. Drizzle with lemon juice and remaining 3 Tbsp. olive oil, and toss to coat. Add salt and pepper to taste. Serve immediately with toasted bread cubes.
*Ciabatta, focaccia, or country white bread may be substituted.