We found this Fatz's Burger when I searched "recommended restaurant in Koenji". That day I do fancy some American taste so we went there. Fatz's Burger located at north part of JR Koenji station, if you have google map, it isn't that difficult to find it. (Address: 東京都杉並区高円寺北3-21-19 ライオンズプラザ高円寺E号.)
We ordered a burger (Single beef + Avocado) and a hot dog (I forgot what I added on my hotdog lol, maybe its chilli beans). The fries comes with the dish tastes so good! I like this kind of real fries more than McDonalds' skinny style.
The only thing you need to be aware is the food is cooking in front of you, which is cool. However, because of the restaurant is small, so you will get the smell on your clothes and hair etc. This is the only thing I don't like when you eating in Japanese style restaurant. You can get some spy at the drug store here to get rid of this kind of smell, I probably will get one this week, as the weather getting cold, my coats are super easy to absorb those smells.
The size of the restaurant is very small but welcome, there are maybe 10 counter seats in total. The chief is a typical American man, very cute and kind. :D They also provide English menu so if you worried about Japanese, then it is not a problem. The main dish comes with bread, coleslaw and fries. You can choose the bread you like (hamburger buns, sandwich bread and hot dog roll). Then you can add vegetables, meat, sauce, topping and side menu. The price will be different according to how you gonna personalise your burger.
Except that, I was totally satisfied with the taste of my hotdog at Fatz's Burger. Not like those "American burger shops" in Roppongi, Azabu-juban, Meguro or other "expensive" area. They usually spend a lot of money on American inspired interior design and charge the customer a stupid price for a burger. Compare with those restaurants, Fatz's burger makes me feel more like a place that you can actually enjoy the real food. I personally prefer the true taste of a restaurant more than the look of a restaurant. That's why I don't really go to those fancy restaurant but often go to those local Japanese style places to eat. At that kind of places, you can learn and know real local people and the culture of the country.
For Fatz's Burger, even it is small and not in fancy places. However, you can still tell that the owner of it spend sometimes to consider how to design his shop. All the displays are burger relevant.
I will give it maybe 8.5/10, if they can improve little bit about the smoke problem, it will be great.