Rinse the sushi rice under cold water until the water runs clear.

Combine the rinsed rice and water in your rice cooker or pot and cook according to the rice cooker's instructions or bring to a boil, then simmer on low for about 18 minutes.

In a bowl, mix the drained tuna with mayonnaise, soy sauce, and rice vinegar.

Once the rice is cooked, let it cool slightly, then add salt to taste and mix gently.

Lay a piece of plastic wrap on your work surface, scoop a portion of rice onto the wrap, and make a small indentation in the center.

Place a spoonful of the tuna mixture into the indentation.

Wrap the plastic around the rice and press firmly to form a triangle shape.

Unwrap the onigiri and wrap a strip of nori around each rice ball.