Preheat the oven to 350°. Wash the beets and while still wet, wrap them individually in foil. Set them on a baking sheet and bake for 1 hour and 15 minutes, or until tender when pierced. Rub the skins off the warm beets with paper towels. Slice the beets crosswise 1/4 inch thick, then stack the slices and cut them into 1/4-inch strips.
In a medium bowl, mix the vinegar and ginger. Season with salt and pepper. Slowly whisk in the oil. Add the beets, toss to coat and let marinate for at least 30 minutes. Garnish with the chives and serve at room temperature.