Heat oven to 400°F. Wrap each beet in foil and roast for 45-60 minutes or until soft. When cool, peel off the skins and chop into small wedges. Place in a bowl.
To make the vinaigrette: in a small bowl, whisk the orange juice, honey, vinegar, olive oil, mustard, and salt.
In a small skillet, brown the walnuts over low heat (about 5 minutes). Add a tablespoon of honey or maple syrup and toss until coated and slightly crispy (be careful not to burn). Remove from pan and set aside to cool.
Combine beets, vinaigrette, salad greens, and nuts and serve immediately.