Add ½ cup of sushi vinegar to the sushi rice and mix well.
In a bowl, mix the eggs, water, flour and salt.
In a large pan, pour in the eggs and fry under low heat until the base is set. Fold the egg in half and flip to the other side. Allow it to continue frying until all of the egg is set. Remove from pan and cut into strips.
Set a sheet of seaweed on a sushi mat and put some rice just 2cm above the bottom of the mat. On the rice, place a strip of egg and some tuna on the rice.
Take the seaweed from the bottom and wrap it around the rice firmly. Continue rolling until the sheet of seaweed is used up. Cut cross-sectionally into 1 cm thick pieces. Serve.