Brush toasted bread with 2 tablespoons oil; season with salt and pepper. Break into 1-inch pieces. Transfer to a large bowl and add tomatoes, zucchini, lettuce, and olives; season with salt and pepper.
Combine herbs, garlic, vinegar, water, and remaining 4 tablespoons oil in a food processor and pulse until smooth; season with salt and pepper. Drizzle salad with 1/4 cup dressing and toss. Serve with remaining dressing on the side.