Egg salad, on its own is usually bland and boring, to say the least. Many European chefs use it simply as a spread for other things on sandwiches. Here, we've taken it to a new dimension, replacing mayonnaise with avocado. This flavorful blending, with caramelized onions to provide added aromatic qualities provides an extraordinary blending of flavors and a sublime result. This luscious sandwich may also be served on a roll, such as a Kaiser, or on a dark bread like pumpernickel.