Korinbo is the place to go to if you're in the mood for some homestyle cooking. The owner is a friendly Taiwanese lady (incidentally her brother is world-renowned artist TF Chen) and coming to eat here is like being served a meal at her home. The menu is fairly limited consisting of maybe 5-6 items but it is all very good and all vegetarian. I'm not sure if the owner speaks English but the menu items are all accompanied with pictures. I recommend trying their teishoku or higaeri set meals. Adding to the homely feel is the space, which is tiny. It seats maybe 6 at most, seated around a counter, so it's not a place to go to if you're in a large group. I've been coming to Korinbo for over five years and it's always on my list of places to go whenever I'm in Tokyo. It's located in Nakano Broadway mall which is a mecca for anime/tokusatsu geeks if you're into that sort of thing.
It's a little hard to find, but here are rough directions: Get off at Nakano station and take the north exit. Follow the path 50m to the brightly lit walkway of covered shops and continue walking for another 200-300m. Eventually you'll see a sign overhead for Nakano Broadway and an escalator. Don't take the escalator as it goes to the 3rd floor. Instead veer right and take the stairs to the 2nd floor. Head to the NW corner of the mall. If you have trouble finding it, look for 香林坊 on the mall map.Pros: friendly staff, good value