Rick Bayless has Tortas Frontera,
there is a Brown Sugar Bakery,
and a Publican Tavern
all those places are respected locally, but they are a lil expensive for me at ORD so I havent tried any of them
i'm more likely to grab some popcorn from Garrett (since i'm coming to the airport from home I dont usually need a meal)
if you are in a big hurry, i think the Farmer's Fridge vending machines aren't bad at all