We have office parties all the time, and the office favorite, hands down, is Mexican food from Lauriol Plaza. We get do-it-yourself fajita and nachos platters, which comes with thick cuts of grilled steak and chicken breast marininated in lime juice, thick flour tortillas, homemade chunky guacamole, a delicious roasted chili salsa and all the usual fixins. It's definitely not authentic Mexican food, but it has a certain Baja Fresh/Chipotle quality about it -- clean taste, but full of flavor. This menu and pricing is super takeout and catering-friendly, so I highly recommend this place for your next office party.
If you don't want to order enough fajitas for your entire office, you should consider going into their humongous sit-down restaurant on 18th St. There are tons of other Mexican offerings on the menu, from enchiladas to chimichangas, plus a brunch menu on Sundays.