Thinly slice the red onion and place in a low bowl.
In a separate bowl, stir the olive oil, red wine vinegar and dried oregano together to combine well. Pour the mixture over the onions, making sure they are submerged.
Let sit on counter at room temperature to marinate for at least an hour.
Keeps for two days unrefrigerated.
Recipe Notes
Adapted from No Crumbs Left (www.nocrumbsleft.net)