Preheat oven to 400 degrees F. Place beets in a 3-quart rectangular baking dish. In a small bowl whisk together the balsamic vinegar, olive oil, and honey. Pour over beets. Sprinkle with salt and pepper. Cover and roast in a 400 degrees F oven for 40 minutes or until beets are tender when pierced with a knife.
On a platter combine watercress, quinoa, and beets. Drizzle with the roasting liquid. Top with chopped tarragon.