Rinse the sushi rice thoroughly, then cook it in a pot or rice cooker according to package instructions. Once cooked, mix in rice wine vinegar and a pinch of salt. Let the rice cool to slightly warm or room temperature.

Drain the canned tuna or salmon and transfer it to a bowl. Add sriracha and Kewpie mayo, mixing until well combined. Adjust with a pinch of salt if needed.

Rehydrate one square sheet of rice paper in warm water, then place it on a flat surface. Rehydrate a second sheet and layer it on top of the first. Place a sheet of nori on top of the rice paper. Using scissors, cut a single slit from the center of the bottom edge of the square to the middle.

Spread a thin layer of tuna or salmon mixture on the bottom left section of the rice paper and nori. Add thinly sliced cucumber and avocado to the top left section. Spread an even ½-inch layer of rice over the top and bottom right sections.

To fold, start with the bottom left section and fold it upwards. Fold the pouch to the right, then fold it down to form a compact sushi sandwich.

Heat a generous amount of neutral oil in a pan over medium heat. Add the sushi sandwiches and fry for 3-4 minutes on one side until crispy. Flip and fry the other side for another 3-4 minutes

Serve warm with spicy mayo sauce on the side.