While Bobby Flay's Mesa Grill is a bit uneven overall (and don't expect to see Mr. Flay here when there aren't TV cameras following him), I will say this: they have one of the best burgers in a town full of very good burgers.
An almost baseball-like hand shaped charcoal grilled patty, sits under two melted cheeses, grill-smothered white onion tomato and leaf lettuce on--surprisingly--an untoasted, fairly bland bun. Clearly the flavors within (and everything augments the juicy, smoky burger, nothing overwhelms) don't need any help.
I recommend you request the crispy, slightly spicy "Adobo fries" which normally come with the (sloppy, confusing) Media Noche burger, instead of the "Southwest fries" which usually come with the regular burger.