In a microwave safe bowl, add vinegar, sugar and salt. Microwave for 30 seconds - 1 minute and stir to dissolve sugar and salt. Transfer liquid to a mason jar.
For quick pickling, boil water and drizzle over red onions in a colander.
Add onions and peppercorn to the mason jar filled with liquid. Optional to add other spices.
Cover with lid and refrigerate for 30 min for best results. Keep refrigerated for up to 2 weeks.