Preheat your oven to 400°F.
While you're waiting for the oven to heat up, combine all the dressing ingredients in a glass bowl and whisk together until well incorporated. Set aside.
Wash and dry beets. Wrap in aluminum foil, sprinkling each beet generously with salt.
Place beets on a rimmed baking sheet making sure foil ends are facing up so juices don't drip out too much.
Roast beets in preheated oven for about an hour, or until tender.
Remove the beets from the oven let cool until they are easy to handle. Run them under cold water and they will peel easily.
Cut beets into slices and strips.
Add Arugula and mixed field greens in a medium-sized bowl.
Add vinaigrette to taste and mix until greens are lightly covered with the dressing.
Place salad on a chilled serving platter and top with sliced roasted beets, orange slices, sliced fennel, and walnuts.
Add a little of the beet strips and a couple of walnuts on top for a pretty presentation.
Optional: The fennel fronds also make a nice garnish and are really tender and flavorful.