Again, this is not a recipe per se but just a description of how I assembled the dish.
Tuna: From a pound block of tuna sashimi, I sliced red meat or 赤身 in relatively thin slices like one would use to make nigiri sushi. I smeared on a small amount of real wasabi exactly like I would do to make nigiri sushi.
Sushi rice: Since this was a lunch, I did not make fresh rice. I microwaved frozen rice in a silicon container and added sushi vinegar (from the bottle). After mixing, I put the lid back on the container and let it steep for a few minutes so that the sushi vinegar was nicely absorbed.
I placed the sushi rice in the bowls and placed the tuna sashimi (with wasabi smeared side down). Since I had a nicely ripe avocado, I sliced it and placed next to the tuna. I sprinkled soy sauce on the top and garnished with roasted white sesame and nori strips.