There are lots of ways to vary this basic idea, still in keeping with the Mexican spirit: bacon instead of ham, a different cheese, a dash of Tabasco or lime juice on the bean patty, add a little avocado, etc. Just let your imagination and preferences guide you.
If you are fortunate enough to be in Brest, France, trot along to the remarkable "Pen ar bread
" bakery in Guipavas, run by Sébastien and Audrey. I recommend it wholeheartedly (Brittany's best bakery in 2019). Here you'll find a whole range of delicious burger buns, like the ones shown in the photos. The owner is a really nice guy and a fount of knowledge about the science of baking, and happy to talk about it.