A Delta flight attendant gave me an important tip about O'Hare a few years ago---the United wing has great food. So I headed down the connector and perused my options. I decided to try Tortas Frontera, the ORD outpost of the Rick Bayless empire.
Here is my Cubano, with ham, cheese, and avocado on that great smushed bread. The sandwich was hearty and filling without being too big. I particularly enjoyed the sauce, which I used as a dip given my lack of a table. It combined an immediate zing with a nice, slow burn that lasted for several minutes.