I have had pickled red onion when I have been out for meals at Wahaca and Wagamama. It was something that I had thought about making myself. I have had success in making quick pickled peppers for salads, so thought I could do it.
I thinly sliced a red onion and then added salt, white wine vinegar and a small amount of sugar. I then added some dried Italian herbs as well.
This I then left for a few hours. I then drained it in a sieve and served with a salad. It was rather nice.