I can't believe I've missed this tiny house serving a limited menu of mandu and kimbap right in the heart of Annandale. It is located in the parking lot across from the Giant, and has been operating there for five years.
The mandu are the best you're likely to find. I had the regular mandu, the big ones are not always ready/available by lunch. Everything here is made fresh daily. The kimchi is at the very top. Excellent. The kimbap (think maki roll) is very well crafted. It is teardrop shaped and holds together nicely. The menu translations are not always accurate (the 'tempura' kimbap is actually fishcake). They have a few other items like rice cakes, tofu, and noodles, which I did not have. Outrageously high quality on what I tried. Most prices are in the $6/7 range.
If you come for the mandu you will leave happy.