These Balsamic Pickled Onions are tangy and slightly sweet, made with just 5 simple ingredients. They're quick, easy to make, and add a delicious crunch to tacos, burgers, and more.

Add the balsamic vinegar and cook over moderate heat, stirring occasionally, until it has evaporated, about 10 minutes. Discard the oregano sprig and season the onion with salt and pepper.