Dice the potatoes into 1cm cubes and soak them in water. Mince the onion and drain the tuna.

Place the potatoes and onion in a microwave-safe container, cover loosely with plastic wrap, and microwave at 600W for 5 minutes.

Mix the cooked potatoes and onion with cream cheese, tuna, yuzu kosho, and a pinch of salt and pepper.

Place the filling onto spring roll wrappers, roll tightly, and seal the edges with the flour-water mixture.