I've had them on a ham, cheese, tomato, mayo, dijon sandwich and they added great acidity and crunch. Place the peeled onions in a glass or ceramic bowl and cover with cold water. Red onions, white vinegar, water, cane sugar, and sea salt. There are countless uses for pickled onions. It really livens up the avocado toast and the tangy pickled red onions are the perfect contrast to the rich, creamy avocado.
