Preheat your oven to 400 degrees. Rinse and pat dry each beet. Wrap each beet individually in foil. Place the wrapped beets on a cookie sheet or oven proof container, and roast for approximately 1 hr.
Remove from oven, and carefully check to ensure the beet is cooked through by piercing with a fork. If the fork is able to penetrate all the way through, the beet is ready. Open the foil, and allow the beets to completely cool. Once cool, you can peel the skin off very easily. You may want to use disposable gloves to keep your hands from staining. Slice each beet into thin slices.
Arrange spinach on a salad plate and add enough sliced beets to your liking. Add salt and pepper to taste, and finish with a splash or two of balsamic vinegar. Sprinkle some shredded parmesan cheese if desired.
You may have more beets than needed for your salad, so you can enjoy them over the course of a few days as a healthy snack!