Place the beets on a large piece of aluminum foil. Drizzle the olive oil on top and sprinkle them with sea salt. Wrap the foil tightly around the beets and place on a baking sheet. Roast for 65-70 minutes, or until they pierce easily with a knife all the way through to the center.
Once the beets are cool enough to handle, rub the skins off using a clean towel or cloth and cut them into cubes.
In a large mixing bowl, combine the remaining ingredients. Add the cubed beets and toss to coat with the dressing.
Garnish with the pistachios before serving.
Notes
* I prefer a little more horseradish in this recipe (closer to 1/4 cup), but I would start here and adjust to your taste.