Had a lovely lunch here yesterday - you can choose between two teishoku (set meal) or a rice dish which are 1200 and 800 yen respectively. These change weekly. My friend had a gyoza set and I had spring rolls. The presentation is amazing, your food comes out in a big tray with lots of little sections containing various dishes, plus miso soup and your drink of choice and a (very) small selection of cookies/cake. Both our meals were very tasty and the volume was good for the price. No English spoken but the staff were very friendly and I'm sure would help out if you need the menu explained.
I was also happy to be able to pick up some dried soy meat at the little shop, they have a good selection and prices are reasonable. Will definitely go back!
The restaurant is a little difficult to find - my best directions (as of November 2014) would be: come out of the north exit of Okubo station and cross the street. Turn right and walk along the street, past a 7-11 convenience store. Take the next proper street on the left (not the small lane which is a dead-end) and walk 20m or so up the road. The restaurant is located at the rear of a complex of a buddhist sect that houses a Miroku buddha (happy buddha).
Cons: Tricky to find, Generally only open for lunch