Combine all dressing ingredients in a blender and blend until smooth. Transfer to a small jar. Refrigerate until serving.
Preheat oven to 375ºF. Add bread to a bowl and drizzle with olive oil. Season with salt and pepper. Toss to coat. Spread evenly on a small baking sheet and bake for 8-10 minutes, until golden and toasted. Cool bread at room temperature while assembling salad.
Spread mixed greens in a serving bowl and top with tomatoes, cucumber, toasted bread, red onion and walnuts. Drizzle dressing on top and serve right away.