Combine vinegar, sugar, and salt in a pint sized jar or small bowl.
Microwave for 45 to 60 seconds, or until hot. Stir until sugar and salt are dissolved.
Add red onions, pressing down to make sure they are covered in the brine.
Refrigerate onions for one hour or until you're ready to eat them. Enjoy!
Notes
You can eat the onions as soon as 30 minutes after making them, but they're better after resting for an hour or longer.Leftover onions can be stored in the refrigerator for up to two weeks.Check out the info before this recipe card for helpful tips, serving suggestions, and more!