Quick Pickled Red Onions

1) Heat the vinegar mixture. In a small saucepan, stir together the vinegar, water, salt and sugar. Cook over medium-high heat until the mixture reaches a simmer. 2) Into a pint mason jar, add the onions. Pour the hot vinegar mixture over the onions, screw on the lid, and shake the onions briefly until they are evenly coated with the vinegar mixture. 3) Let the onions marinate for 30 minutes, making sure that all of the onions are fully submerged in the vinegar mixture.