1) Preheat the oven to 180C/Gas 4.
2) In a small bowl, combine the olive oil, salt, and pepper. Brush the beets with the olive oil mixture, then wrap them in aluminum foil and arrange on a baking sheet. Bake until fork tender, about 1 hour and 15 minutes. Remove from the oven and let cool in the foil. Slice the beets and set aside.
3) Evenly divide the salad greens, orange sections, walnuts, goat cheese, red onion, and beets between 4 salad plates. Top each salad with 2 tablespoons of cacao nibs. Drizzle with Cocoa Vinaigrette just before serving.
4) In a small bowl, add the vinegar, cocoa powder, sugar, salt, and pepper and whisk until smooth. Slowly add the oil, whisking constantly, until blended.