As a Southern Californian, probably my biggest complaint with living in China is lack of Mexican food. In LA, the cheap "street food" is Mexicans in a taco truck equipped with a full kitchen.
As for Mexican fast food, Taco Bell is about as authentic as Panda Express is for Chinese food, but myself and all my friends fell in love with Chipotle. It's basically like Subway, but for burritos instead of sandwiches. Pretty high quality, delicious, have-it-your-way, and cheap. Last time I went home, Chipotle was the first stop after the airport.
As for the Mexican restaurants in Beijing, they're all expensive and severely lacking. Chinese people just can't do it right. Mexican food needs shit tons of dairy products, which are always expensive in China, so managers constantly skimp on the cheese and sour cream, so it usually just sucks.
So someone just opened a Chiptole clone in Wudaokou. Some friends and I wandered in there last night to give it a try. The manager is this American-Chinese girl. Never before in China have I had an conversation with the proprietor of a restaurant.
Anyway, she really is trying to make it like Chipotle, and she's on the right track. My biggest complaints were lack of sour cream (American Chipotle just pours the stuff on), and no chance to instruct the burrito-maker on what to put in it, so I got a bunch of peppers I don't really like. My friend went back for seconds.
This girl rented a big space in Wudaokou, the place is brand new, huge, and really nicely-decorated. AND, it's cheaper than almost every other Mexican place in China. The full "meal" with drink is barely over 30rmb. Frankly, I can't imagine that this restaurant endeavor is going to survive (Chinese people just can't get into Mexican), so I'm asking you, WLIB Wudaokouers (I'm looking at you, Pete Mcbrostein), to go try it. I prefer that the restaurant survives as long as possible because I like that kind of food, but I can't support it alone.
(I think I was the lone supporter of Doritos' foray into Chinese supermarkets, and although I absolutely cleaned out every store I could find, Doritos are already gone.)
It's maybe 200 meters west of the Wudaokou subway, north side of the street, just past the KFC, walking towards Google/Microsoft buildings. The name is "The Avocado Tree."
I swear I'm not affiliated with them whatsoever.