Preheat oven to 450°.
Leave root and 1 inch of stem on beets; scrub with a brush. Place beets in a 13 x 9-inch baking dish; add 1/2 cup water to dish. Cover and bake at 450° for 40 minutes or until tender. Drain and rinse with cold water. Drain; cool. Trim off beet roots; rub off skins. Slice each beet into 8 wedges.
Combine beets, onion, and remaining ingredients in a bowl, stirring gently.