Cook rice and let it cool slightly in a bowl. Mix in sesame oil and salt.
In a separate bowl, combine drained tuna, Kewpie mayo, Sriracha, and a pinch of salt.
Place a nori sheet on a cutting board. Spread a layer of rice in the center.
Add the tuna mixture, followed by cucumber and avocado slices.
Top with another thin layer of rice and a small ΒΌ sheet of nori.
Dab a little rice on the corners of the nori to help it stick.
Fold the corners toward the center, wrapping the filling completely.
Wrap tightly in plastic wrap and let it sit for a few minutes.
Slice in half and enjoy!