A day late I went and tried RST's discovery with my adventuresome Mexican-chowfriend (I mean, he likes authentic Mex, not that he is), on its desolate strip of Kimball across from the El terminus and next to a Burger King, and realized that I had even seen it once after dropping someone off at the El and had a passing thought about "who can tell if a joint like that is good or terrible?"
It's pretty good and nicer and more professional feeling on the inside than out. I wasn't ecstatic about it but I found the homemadeness entirely likable. This is the kind of food that has to be eaten hot, and everything I had was an argument for freshly made hot corn tortillas. (I have to admit if it comes from a package, I'd much rather have a flour one than the usual corn rubber. Call me a gringo.) The most interesting and delectable item was, indeed, the quesadilla flor de calabaza (did I get that right?); I believe the squash was sauteed, and I'll have to try one where it isn't because it seemed to need that. But the combination of different squashes gave a range of flavors (from peppery to spinachy) that I wouldn't have credited squash with normally. (There may actually have been some of those things in it.)
I also had a taco al pastor, which was not too fatty (for $1.65, quite lean) and amusingly tasted very much like a dim sum pork bun (same pepper sauce?), and huarache, which was hearty but didn't come together for me (bean flavor was sort of lost between corn and salsa). The only thing I found outright disappointing was the pina agua fresca, which seemed to be canned pineapple juice watered down. Is there some place that's known for really good agua fresca? It's the sort of thing I'd order more if I believed I'd get something really good a greater proportion of the time.
And you brains fans-- they were pushing a brain taco special today.
So anyway, thanks RST, and thanks Chowhound for existing to tell me about such places! Now can I learn the name of your secret Iraqi place?