My fav burger hole in wall in San Antonio is Chris Madrid's, which has a slight Tex Mex twist on the burgers. I ran into Meg Ryan there back when she was married to Dennis Quaid and living near SA. Back then it was just a shack with about 15 seats.
They serve a bean burger, which is actually refried beans with the burger. Or the Flamin' Jalapeno aka, the Flamin' A S S burger.
Also served is pico de gallo for putting on your burger. It makes the burger!