Peel and cut satoimo into bite-sized pieces. Sprinkle with salt, rub gently, rinse with water, and drain. Place satoimo and 2 tbsp water in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for about 5 minutes until tender. Drain and mash coarsely.

In a bowl, mix the mashed satoimo with the tuna, cheese, mayonnaise, and salt and pepper. Divide the mixture into 8 portions.

Place a shiso leaf on each spring roll wrapper, add the filling, and wrap tightly. Seal the edges with the flour-water mixture.