I think Monjya is special food from Tokyo.
Do you know Okonomiyaki? It is a pancake with vegetable and meat or seafood or even chees as you like. Then Monja is almost same but more liquid.
I heard its coming from Tokyo and not a lot of place in Japan will offer that.
Most famous Monja town is Tsukishima which is close to Ginza.
Here is the site! http://www.monja.gr.jp/ (sorry only in Japanese)