This is a year later, but one thing to note for these recipes is that Japanese bell peppers (piiman) are different than the big fist-sized bell peppers you might see in western cooking. So when it says 8 bell peppers for the Umashio bell pepper recipes, it means a much smaller pepper, probably a half to a third of the size of big boy bell peppers (you can see the size relative to his hand on pg 6). Same common ancestor pepper (native to Americas and imported to Japan mid to late 1800s), with thinner walls and much smaller, usually about the size of a jalapeno or bell pepper.
What I'm getting at is don't use 8 huge bell peppers if you try this recipe. That is too much pepper.