Cut each nori sheet into 4 strips and set aside.
In a mixing bowl, combine the drained tuna, mayonnaise, and soy sauce. Mix until smooth and well combined.
Next, place a sheet of plastic wrap on a cutting board and sprinkle a pinch of salt on top. After that, spread cooked rice on the plastic wrap into a rectangle (about 6 x 3 inches).
Place about 1 tablespoon of the tuna mixture on the top half of the rice rectangle. Then, fold the bottom half of the rice over the tuna to sandwich the filling.
Using the plastic wrap, gently shape the rice into a triangle. Rotate and repeat with the other sides so it forms a firm triangle.
Finally wrap a strip of nori around the rice triangle. Then, press gently to stick it to the rice. Repeat with remaining rice and tuna mixture.