Winghart's is a great (somewhat) new restaurant in Market Square with excellent burgers and fries. My favorite is the Shipwreck Burger (cool name, cool guy) and their fries. Great beer and whiskey selection as-well.
This restaurant was hugely popular during the lunch rush over the summer and caused me to unfortunately not visit very frequently due to the amount of time required to have lunch. They've opened some dining space upstairs and appear to be doing a bit better turning meals around in the kitchen. Hopefully they'll keep improving their speed and this place will become a go-to for a quick (and delicious) lunch.
Recommend the Shipwreck burger, the Pittsburgh salad with chicken patty, or the Winghart-attach pizza. Good stuff.