Combine the vinegar with sugar and Mexican oregano in a saucepan and bring it to a boil.
Add in the bay leaf and lime juice and turn off the heat.
Add the onion slices and jalapenos in a glass jar and pour the hot brine over it.
Let it sit at room temperature for an hour and then refrigerate.
Notes
You could also try using white onions or yellow onions instead of the red onions that I used for the recipe. Remember that if you use different onions, you won’t get that bright pink color.You could also choose to use distilled white vinegar instead of apple cider vinegar if that’s what you have at hand. Red wine vinegar is another good option. These quick Mexican pickled onions will last for up to a week when refrigerated properly, if not longer. Just make sure you add your onions into the jar when you’re ready to add the pickling liquid, and add enough brine to ensure that the onions are fully submerged. To make the red onion to have the perfect thin slices, I would recommend using a mandolin slicer. To make Mexican pickled onions last longer, remember to pat them dry and then slice and use them for the recipe. The idea is to remove as much moisture as possible.