It's pork schnitzel on a bun with pickles and onions. They call it tenderloin, but it's usually made with pork loin (not tenderloin) pound it out flat.
I used to go to a client golf tournament every year in Indiana and they always served these things. I found them to be kind of like most of Indiana -- very milquetoast-y and bland.
I say "most" because the cocktail sauce at St. Elmo's is the exception.