In a small pot, combine water, vinegar, sugar and salt and heat until dissolved. You can also combine in a microwave-safe bowl and heat until the sugar and salt are dissolved. Add in any other seasonings.
Place sliced onions in a medium bowl, quart-sized jar or split between two pint jars. Pour pickling liquid over the onions and either stir or seal the lid and gently shake.
Let onions marinate for at least 30 minutes.
Serve immediately or refrigerate in a sealed container for up to 2 weeks.
Notes
The equipment section above contains affiliate links to products we use and love!PREP AHEAD: Though they can be used right away, I actually recommend making these pickled onions in advance as the flavors meld together after resting for a bit. LEFTOVERS/STORAGE: Serve immediately, or refrigerate in a sealed container (like a mason jaraffiliate) for up to 2 weeks.NUTRITION NOTES: Onions provide loads of flavor as well as fiber and antioxidants such as anthocyanins. FOOD WASTE NOTES: Save the onion skins to make stock. Reuse your pickling liquid to pickle something else!SERVING SUGGESTIONS: Add pickled red onions to tacos, sandwiches, savory breakfast foods and more.