Add the red onion, lime juice, salt, and black pepper to a glass jar or storage container. Cover and stir or shake to combine.
Refrigerate for at least 30 minutes to allow the red onions to cure, stirring or shaking the mixture halfway through so that all the onions are evenly coated with the liquid.
Taste and adjust the salt as needed. Serve immediately or store in the refrigerator for up to 2 weeks.
Notes
This recipe was inspired by Rick Bayless after I saw him using this method of making pickled onions using only lime juice.
Use fresh lime juice: Freshly squeezed lime juice makes all the difference in flavor. Avoid bottled lime juice if possible.
Choose the right container: Glass jars or containers are best because they don’t react with the acidity of the lime juice. I don't recommend using plastic.
Check the color: The onions are ready when they’ve turned a bright fuchsia color.