In a small sauce pan over medium high heat, add vinegar and seasonings. Bring to a rolling boil. Let continue to boil for five minutes.
Put the sliced onions into a mason jar or other container. Pour the hot vinegar mixture over the onions. Make sure that the majority of the onions are submerged. Let sit for at least 30 minutes before using.
If you have any leftovers, you can store them in an airtight container in the refrigerator for up to 5 days.
Keyword garnish, oregano, pickled onion, red onion, red wine vinegar