1. Preheat oven to 425°F. Remove greens and bottom roots from beets. Wrap beets with foil. Roast 45 to 60 minutes or until beets are tender when pierced with small knife. Cool until able to handle. Peel beets and cut into slices.
2. Meanwhile, trim base from fennel bulb. Reserve fennel fronds for garnish. Cut fennel into wedges. Toss with 2 tablespoons of the oil. Arrange fennel in single layer on foil-lined shallow baking pan sprayed with no stick cooking spray. Roast fennel 25 to 30 minutes, turning halfway through cook time. Cool.
3. Mix remaining 6 tablespoons oil, vinegar, tarragon, vanilla, sea salt, sugar and pepper in small bowl with wire whisk until well blended. Divide greens, oranges, beets, fennel and red onion among 6 salad plates. Serve with dressing. Garnish with fennel fronds, if desired.