Stir together the cider vinegar, salt, honey and peppercorns. Heat this to a boil either on the stovetop or the microwave. Stir to make sure the honey and salt have dissolved.
Pour brine mixture over sliced red onion rings. Allow the mixture to sit out at room temperature for about one hour.
Transfer to a covered container and refrigerate. They will keep in the fridge for up to 2 weeks.
Try these pickled onions on: salads, tacos, burgers, sandwiches, or even eggs!