Updated: Aug 2
There is a Sushi called "Mushi Zushi" in Japan. The word Mushi comes from Musu (to steam) in Japanese. So the literal translation is Steamed Sushi.
It's a regional style of cooked Sushi originated in Osaka, Kyoto and served in some other regions west of Osaka, typically during the winter months from December to March.
As it's a "very" regional dish, if you ask any Japanese, it's likely that most of them have never heard of or seen this Sushi, unless of course, they are from the Osaka and Kyoto region.
I learned about this dish only a few years ago from a Japanese TV show.
Mushi Zushi comes in either a bowl or a bamboo steamer, with such fish as Anago (sea eel), Unagi (freshwater eel), Shrimp and white fish like Tai Snapper with Shitake mushroom and cooked shredded egg over Sushi rice.
Mushi Zushi can be classified as a steamed version of Chirashi.
The recipe is quite simple - just place any kind of fish and pre-cooked vegetables over Sushi rice and steam until the fish is cooked.