Adapted from The Kitchn
Flake cooked fish with a fork and mix with the rice and sesame seeds.
Wet hands then place one quarter of the rice mixture (about 3/4 cup) in your hands and squeeze firmly. Rotate and squeeze until it forms a triangular or circular shape that holds together securely. Wrap a strip of nori around the middle. Repeat with remaining rice mixture.
Alternatively: Place about 3/4 of rice mixture inside a piece of plastic wrap, squeeze mixture together tightly and then shape.