Preheat the oven to 350°F.
Scrub the beets with a wire vegetable brush (or a clean piece of soap-less steel wool).
Cut each beet in half from pole to pole and then into thick wedges. You should get 8-10 wedges per beet.
Pour oil on a large baking sheet and spread the beets evenly on the sheet. Sprinkle salt over beets and turn them over so both sides are coated with oil.
Roast for 45 minutes to an hour, or until the beets are tender. (Time varies a lot based on the age of the beets.) Remove beets from the oven and let them come to room temperature.
You can roast the beets a few hours ahead of time. Just let them sit at room temperature until you’re ready to toss the salad. You can drain them on paper towels to get rid of some of the excess oil.
Combine dressing ingredients in a small cup and mix well.
When the beets are cool, put the spinach, pecans, and cheese in a large bowl and toss with the dressing.
Arrange the salad on a platter and surround it with beets.