I love avocado and guacamole on burgers and sandwiches, so much so that I often suspend my thrifty disposition and splurge by adding avocado. Mayo is OK in light amounts. As a child, my sandwiches were always prepared with butter (baloney and butter, deviled ham and butter, etc.) and I always wished my mom would just buy us a jar of mayo.
To contribute to the DotM thread, I had Fred 62’s (on Vermont in Los Felix) veggie burger and found it quite delicious. Flavorful homemade patty that wasn’t beany (not my veggie burger preference) with avocado (yay!), the usual lettuce, tomato, and onions, all on a brioche bun. Served with a pickle. Unfortunately fries or a side cost extra.