I LOVE pickled onions! ... HOWEVER! They need to be super fresh, relatively young and thinly sliced.
Onions are the third most consumed vegetable in the United States (behind potatoes and tomatoes)
. As a result, they tend to be heavily mass produced. As a result of their durability and capacity to stay edible for several months, unrefrigerated, many onions are REALLY pushing the edge of "fresh", by the time they get home. An older onion is FAR more likely to make you cry when you cut it. It'll have that strong ... funky ... ONIONY flavor, which is something I personally detest (much in the same way I LOVE super clean fresh fish, but LOATHE that old "fishy" smell)
Look for onions with thin "tissue-like" skins, no bruises or blemishes and which are free of cuts. The necks should be clean and dry. If they have any wet spots, discolorations or soft mushy bits ... move on!
A good, fresh onion will slice clean and have virtually no odor. With a sharp knife, you should not cry. The taste should be quite sweet, without the slightly bitter "heat", which can come from an old onion. The best bet is to get them at a Farmer's market, where they were very likely harvested within the previous 48 hours!
When using onions for pickling, or caramelizing, slice them from top to bottom, rather than side-to-side. This will help them stay intact, rather than turning into a pile of mush. In this particular instance, thinner is better! Let them sit and marinate for at least 30 minutes, but ... overnight is better! They will take on a beautiful magenta hue!
Finally, these delightfully tart, slightly sweet and somewhat spicy pickled onions are PERFECT as a topping on a Cochinita Pibil Taco
, with Cheddar Taco Shell
. They're also great as a garnish in soups, as well as thrown into most salads! They have a strong flavor, but ... one that tends to complement many dishes.