Slice the chikuwa in half lengthwise, then in half crosswise. Combine the chopped mentaiko and mayonnaise (use aluminum foil cups to reduce dirty dishes).
Place 2 each into the foil cups. Fill the crevice of the chikuwa with the "mentai-mayo" mixture from step 1.
Top with cheese and bake for roughly 5 minutes in a oven.
It's ready to eat when the cheese is melting and slightly browned. Pack into bentos after they cool.
When I have leftover mentai-mayo, I toss it with frozen french fries that I usually break apart with my hands, which are baked in the oven.
Story Behind this Recipe
When I was having coffee with friends who are also moms, we started talking about food for bentos. That's when I came up with this recipe. My son loves mentaiko, so I usually pack all sorts of mentai-mayo food in his bento.
Because the two pieces will be stuck together (as seen in the photo of step 4), I recommend you break them apart before adding into bentos. If you leave them stuck together, the cheese for the other piece will come off when you try to eat one chikuwa.