Provided by: Chef Vincent Scotto
With a paring knife, cut the ends off the beets and trim any roots. Scrub the beets, cut each beet in half, and cut each half into 3 equal pieces. Place the beets in a large bowl and toss with the onion, oil, and vinegar; then season with salt and pepper.
Cut 1 piece of heavy-duty aluminum foil approximately 48 inches long by 24 inches wide. Fold it in half so you have a double thickness 24 inches square. Place the seasoned beets on the foil and fold the foil like an envelope, crimping the edges to seal. Cut four 1-inch vents into the top of the pouch, to release the steam.
Start a medium fire on one side of the grill, and place the beets directly on top of the coals. Cover the grill and roast the beets for 20 to 25 minutes; then turn the pouch around and roast for another 30 minutes. Open one vent just enough to test one piece of beet. It should be tender. If not, roast for an additional 5 minutes.