I dunno about authentic, but Valle Luna serves up some pretty good, greasy, Mexican eats.
The Vallitos and Lunitas are a good appetizer (mini burros and flautas). The fajitas here are pretty good. The chips and salsa is super addicting (love the spicy one), and the guacamole is nice and fresh.
I don't mind coming here when I'm in the mood for some Mexican food, armed with a coupon (they usually come in the mail or in the super shopper/savvy saver/whatever it's called).