Preheat the oven to 400 degrees F.
Wrap the beets in foil packets and roast in the oven until tender, about 1 hour. Open the foil packets and let cool. Once cool enough to handle, peel using a paper towel, then dice.
In a medium bowl, add the olive oil, vinegar, honey, red onions and Dijon and whisk together. Add the beets and spinach to the dressing and toss to coat. Top with the goat cheese and walnuts.