In a small pot over medium heat, or in the microwave oven, heat up the vinegar to almost a simmer. Add the rest of the ingredients except for the onion slices. Remove from the heat.
Place the onion slices in a jar with a lid. Pour the pickling juices over the onions so that they are submerged. Place the lid on it the jar and allow to sit for 30 minutes.
Notes
Use on sandwiches, or in salads, legume / vegetable casseroles, or grain pilafs.