In a large, lidded saute pan, heat 2 TBS of the oil over medium heat. Add the onion and cook until soft, 6-8 minutes. Add the beets and *salt and toss to combine. Cover and cook for 10-12 minutes, until the beets are completely softened. Add the vinegar and toss to combine, scrape up any browned bits with a wooden spoon. Set aside to cool.