OK, it's time for a really tough What Was It? Wednesday. This current Mexican fast food restaurant started out life way back in probably the mid-to-late 1970's as a fast food burger joint. The building has been modified over the years, adding on the eaves and rounding out the top of the roof. Also, the dining room on the right in the picture was originally an open-air patio. The overall appearance of the original structure was very boxy.
The word "boxy" was a huge hint. This was an old Jack In The Box.