Preheat the oven to 400°F.
Cut one orange in half, and zest it. Squeeze the juice into a small bowl, and set aside for now.
Place each beet on its own sheet of aluminum foil, large enough to wrap it in. Drizzle 1-2 tablespoons of oil on them, and sprinkle with the orange zest.
Roast in the oven for 40 minutes, up to an hour depending on size. They should be tender.
In the meantime, blend the saved orange juice, remaining 2 tablespoons oil, honey, lemon juice, mustard, ginger, salt and pepper in a bowl. Blend to create the dressing.
When the beets are done, cut them into slices, and mix with half the salad dressing.
With a sharp knife, cut all the peel and pith from the remaining 3 1/2 oranges, and separate into wedges.
To assemble the salad, place the arugula on the bottom as a bed, then alternate the beet slices and Cara Cara orange.
Top with the walnuts, and drizzle with the rest of the dressing.