menya mappen is a japanese udon/soda bar (more of a bar than resto), with a don-version (rice bowls) next to it. cheap quick and very tasty, it's right next to george st cinemas so that should be pretty close to where you work?
google that, you will find a multitude of reviews (most if not all positive)!
the snag stand in westfield sydney is quite nice, but it, like all the other places in the food court, are a bit (s)wanky - i really can't justify paying 7-9$ for a hot dog.....