Combine red wine vinegar, water, 1/2 teaspoon kosher salt, and sugar or honey in a jar. Add onion and shake to combine. You can let this pickle and soften in the fridge for 1 hour and up to 5 days, but it’s not bad at all in 10 to 15 minutes. To hurry the pickling along, you can actually microwave this (lid off, obviously) for about 20 seconds, and then let it hang out in the fridge until you’re ready.