Open tuna can. Drain it and squeeze out the oil. 

Take stems off perilla leaves. Cut the ¼ piece of onion into thin small slices. Julienne the piece of cucumber and cabbage leaf into very thin strips. 

Take out a mixing bowl. Mix-in mayonnaise, vinegar and black pepper. Stir it together. Then throw in the tuna, cabbage, cucumber and onions. Mix it together with your hands. Top the mixture with a few shakes of black pepper. 

Put rice into a large bowl. Fan it out so it can lose some steam and cool off.

Then sprinkle some salt (½ teaspoon) over the rice. Place sesame oil in (1 Tablespoon). Sprinkle on sesame seeds as well. Mix everything together. Set aside.

Place a sheet of gim on the cutting board (make sure its dry) 

Place an even layer of rice over the gim - up to about ⅔ of the sheet (reference video). Don't let the rice clump up in one spot - spread it out evenly. 

Place two perilla leaves at the center of the rice. Then put a few scoops of the tuna mixture over the leaves. 

Pull the bottom of the sheet up to the ⅔ line. Then use your hands to gently scoot back the filling, while squeezing the roll to make it firm. Continue to roll to the end.

Dab your finger in water. Then run it across the edge of the sheet. Roll it and seal the roll off.

Repeat again to make two more rolls.