Slice the cucumber into 4 long strips. Mix the sushi vinegar ingredients (vinegar, sugar, salt) in a bowl.

Combine the cooked rice with the sushi vinegar mixture, mixing gently to create sushi rice.

Mix the canned tuna with mayonnaise in a bowl to create tuna mayo.

Prepare the egg mixture by combining egg, sake, mirin, and a pinch of salt in a bowl.

Heat a frying pan with a thin layer of salad oil. Pour in the egg mixture and cook until semi-set. Roll the egg and cut into two equal pieces.

Place one sheet of nori on a bamboo mat. Spread half of the sushi rice evenly, leaving 3cm at the top edge uncovered.

Layer half of the lettuce, crab sticks, cucumber, egg roll, and tuna mayo slightly below the center of the rice. Roll tightly from the bottom, pressing gently to secure the filling.