Slice red onion thinly, and any chile peppers(optional) and place in a glass pickling jar.
Heat the vinegar, water, sugar, and salt in a medium saucepan over medium heat. Stir until the sugar and salt dissolve, about 1 minute. Let cool and pour over the onions. Add Mexican oregano to liquid.
Mix well so all of the ingredients are combined.
Cover and place in the refrigerator for 4-6 hours before eating.
Keyword pickled red onions, jalapenos pickled, spicy pickled red onion recipe