No Brine, No Heat: Easy Pickled Onions in Just 15 Minutes! This rapid onion pickling method will give you a flavorful topping perfect for layering on sandwiches and tossing into salads.
Read more here: https://www.seriouseats.com/2016/07/how-to-quick-pickle-even-faster-tame-raw-onions-with-vinegar-condiment.html