This is the very best and easiest recipe that I have found. I think it would work with any onion variety.
Simple Pickled Red Onions Recipe (In Less Than 5 Minutes)
1 medium size red onion
1/2 cup (plus a little extra) white wine vinegar (or
apple cider vinegar)
1 teaspoon salt
Optional: Other seasonings like 1 teaspoon chili powder or garlic powder for flavor
Instructions
Thinly slice the onions, leaving them in rings for easy use.
Carefully place the rings into a pint size jar and sprinkle with the salt and other seasonings.
Pour the vinegar over the rings to fill the jar and put the lid on.
Leave at room temperature for two hours so flavors can meld.
Transfer to the refrigerator for up to two weeks (though ours are usually gone in a couple of days!)
https://wellnessmama.com/127248/pickled-red-onions-recipe/
Her explanation:
Pickled red onions provide all the flavor of fresh red onions, but have extra depth from their pickle-ing and will keep in the fridge for weeks! Even better- you can make them in only five minutes, or let your 5-year-old make them… it is that easy! I keep these guys in the fridge at all times… you know, for pickled onion emergencies.
Ways to Use Pickled Red Onions: On everything.
Want a little more direction? Try these:
Beef Barbacoa– Pickled red onions are amazing on one of our favorite budget-friendly and time saving recipes: Beef Barbacoa. I cook this in a pressure cooker (I use this Instant Pot) in less than an hour for a delicious restaurant-quality dinner on a busy day.
Salads– These spice up almost every salad.
Breakfast– Great on almost any breakfast foods, but especially on quiche, eggs, or other savory foods.
Tacos or Taco Meat– These are especially great on any kind of tacos or taco salad you can come up with!
Burgers– Pickled red onions are a great addition to any burger.
Charcuterie plate– Feeling really fancy? Add these to a charcuterie plate along with your favorite cured meats and cheeses.