Japan has a Ramen Museum, a Curry Museum and now Gyoza Stadium
In Ikebukuro there is an indoor amusement park run by Namco called Namjatown and recently the remodeled a section of it into what they called Gyoza Stadium where they have over 30 kinds of Gyoza. You might know Gyoza as their American name used in many Chinese restaurants in America, "Pot Stickers".
We tried about 16 different kinds. Since they are small it's not so hard. There are like 10 or so storefronts inside so you go up, get some and then try to find a place to sit.
We lucked out with in that there was this small old style room with an old TV running old movie clips from like the 40s or 50s and we walked by just as the previous group was clearing out so we scooped it up.
I'm not sure if this is a temporary thing or not. Probably as long as people are going it will stay. The entrance fee for Namjatown is only 300 yen (about $3) so go check it out!