For the rice: Place cooked white rice into a large bowl and let cool for at least 10 to 15 minutes. Starting with 1 tablespoon, mix in the sesame oil and salt (or Seaweed Gomasio if using). Mix well and taste. Add just a touch more sesame oil if needed but do not overdo it. Your rice only needs a hint of sesame oil for taste. Sprinkle with sesame seeds, mix one last time and set aside.
Step 1: Take one sheet of the dried gim and place onto your bamboo mat (make sure the bamboo sticks are horizontal). Spread about a ½ cup of cooked, seasoned rice onto 2/3 of the gim, spreading it evenly with your fingers. Tip: leave at least one inch uncovered (with no rice at all) at the top. This will help you to seal your roll at the end.
Step 2: Lay in the tuna and then all of the ingredients (bell peppers, carrots and cucumbers) on top, leaving about an inch of exposed rice down at the bottom. Using the bamboo mat on the end closest to you, roll from the bottom up and over the ingredients (like you're rolling a sleeping bag), pressing down gently but firmly to make the fillings stay in. As you continue to roll, pull the mat up and straighten it so that it doesn’t get caught in the roll. Continue until you have reached the edge of the gim.
Step 3: Using your fingers, dab just a little bit of water along the top seam of the dried seaweed and roll to seal it closed. Roll and gently squeeze one last time with the bamboo mat, set aside and continue with the other seaweed sheets.
Step 4: When all of the rolls are finished, using a sharp knife, dip the knife into the water and lift the knife up so the water runs down the blade. This will help you to get a nice, clean cut. Slice each roll into about 8-10 pieces. Sprinkle on some sesame seeds, serve with soy sauce if desired and enjoy!