I remember trying to describe this sushi once on a2k, but I've lost it to that ether, and besides, I liked rereading this thread.
Finally I find a recipe to make it myself, but no way I'd try it in this lousy, er, miserable-for-fish city.
I loved these things, spicy tuna hand rolls, then made at Tomo Deli..
http://www.saveur.com/article/Recipes/Spicy-Tuna-Hand-Roll
Tomo's had sliced fresh raw tuna, not chopped, but otherwise it seems similar. One was enough for lunch, unless I broke down and also ordered some gyoza.
MAKES 8
This Japanese specialty requires very fresh fish.
1 1/2 cups short-grain Japanese rice
1 1/2" piece konbu (dried sea kelp)
2 tbsp. sugar
1 tsp. salt
2 tbsp. rice vinegar
10 oz. very fresh yellowfin or bigeye tuna,
chopped
1 scallion, trimmed and finely chopped
4 tsp. sriracha chile sauce
4 tsp. Asian chili oil
2 tbsp. masago (smelt roe)
4 sheets yaki-nori (toasted seaweed),
halved crosswise
1. Put rice into a medium pot, cover with water, and swish around with your hand until water clouds. Drain; repeat process 3–4 more times, until water remains clear. Drain again, return rice to pot, add sea kelp and 1I cups water, and bring to a boil over medium-high heat. Boil until liquid barely covers rice, 8–10 minutes; cover, reduce heat to medium-low, and steam until rice is tender, 15–20 minutes more; discard sea kelp.
2. Transfer rice to a large bowl. Allow to cool briefly. Dissolve sugar and salt in vinegar in a small bowl, add to rice, and gently stir with a wooden spoon until rice is just warm.
3. Combine tuna, scallions, chile sauce, oil, and roe in a bowl and set aside. Position 1 sheet of seaweed, shiny side down, with long edge parallel to edge of work surface. Spread 1/4 cup of the rice onto left third of seaweed. Spread 2-3 tbsp. of the tuna mixture over rice and tuna on the diagnol. Repeat process with the remaining seaweed, rice, and tuna.
A photo from another site - (Eileen Likes to Eat blog)