The sweetness of beets is a natural match for ginger's spicier side. Beets can be roasted up to 3 days ahead of time; simply bring them to room temperature before serving.
Preheat oven to 425 degrees. Wrap beets in parchment-lined foil and place on a rimmed baking sheet. Roast until tender, 45 to 60 minutes. Let cool briefly, then rub with a paper towel to remove skins. Cut into 3/4-inch wedges.
In a large bowl, whisk together oil, vinegar, and ginger; season with salt and pepper. Toss beets in dressing and sprinkle with pistachios.