Apparently, this is a thing. Oklahoma City Oklahoma

Tucker's Onion Burgers - In the 1920's several cafes in Oklahoma were looking for ways to stretch beef further and began frying their hamburgers pressed with a pile of thinly shredded onions. It worked to help keep their businesses afloat during the Great Depression and the burgers tasted great so fried onion burgers are now a thing in Oklahoma. El Reno, OK is actually The Onion Burger capital of the world! Who knew? There are several of these around, but this one is on NW 23rd Street in Oklahoma City, OK