Combine all the dressing ingredients into a container and blend well. This can be made ahead of time to allow flavors to develop.
Preheat oven to 400F. Wrap beets in foil and roast for about 1 hour until tender. Peel and dice.
Toast the bread slices, cut into cubes and set aside.
Prepare all other ingredients and set aside.
Combine the beets, orange segments, sunflower seeds, herbs and spices in a large bowl.
Toss with half of the dressing. Add salt and pepper to taste.
If eating immediately, add the cubed bread and more dressing. Toss until the bread cubes are coated with dressing.
Sprinkle the pistachios on top along with additional sumac, salt and pepper to taste.
If making this ahead of time, toss with the bread cubes right before serving.