Preheat oven to 450°.
. Line a large baking sheet with foil.
. Cut beets into 8 wedges each. Cut carrots in half lengthwise; cut halves into 3-inch pieces. Remove skin from onion; cut into large wedges, leaving root intact.
. Place beets, carrot, and onion in a medium bowl; drizzle with oil, and toss well. Arrange vegetables in a single layer on prepared pan. Bake at 450° for 15 minutes; stir and bake an additional 10 minutes or until tender.
. Return vegetables to bowl; add vinegar and remaining ingredients. Toss gently to coat.