If you get as far as Tucson here are some options:
LaFuente upscale Mexican
El Charro also upscale, a bit over rated lately
BK Carne Asada fast food, great Mexican hot dogs
Los Nopales not our favorite, but a lot of folks like it.
Mi Nidito have not tried this one yet
Los Portales family style, excellent
Perfecto's great soup, small family run, friendly and popular with the locals, DW says "all the ambiance of a bus station", not open late.
Little Poca Cosa right in the heart of downtown, unusual atmosphere, really good food!