Stack the seaweed sheets together and place a piece of rice paper on top. Cut around the rice paper to get a perfect circle. Set the seaweed trimmings aside for later.
Briefly dip a sheet of rice paper in water, then immediately stick it onto a circular seaweed sheet. Work quickly before the rice paper softens; it is much easier to align while it is still slightly firm. Brush a generous amount of cooking oil across the rice paper side. Repeat this process for the remaining sheets.
Hang the seaweed taco shells over your oven rack bars with the rice paper side facing upward, ensuring you leave gaps between each shell so they don't stick together. Bake at 180°C (350°F) for 15 minutes until crispy.
Thinly slice the cucumber and avocado, then set them aside. Drain the canned spicy tuna through a sieve, pressing down with the back of a spoon to remove any excess liquid.
In a large bowl, combine the cooked sushi rice, sesame oil, a pinch of salt, and 1 teaspoon of sesame seeds. Take the leftover seaweed trimmings from the first step, tear them into tiny pieces by hand, and fold them into the rice. (Note: If you have extra seaweed trimmings left over, save them in the fridge for next time.)
To assemble your tacos, layer the seasoned rice at the bottom of the baked shells. Top with the sliced cucumber, avocado, and spicy tuna. Garnish with extra sesame seeds, chopped spring onions, and a drizzle of Kewpie mayo. Enjoy immediately!
