Prepare the hand water by combining the water and rice vinegar in a medium size bowl.
Preparing the spicy tuna
Mix the filling ingredients in a small bowl.
Preparing the temaki
Cut each sheet of nori in half using scissors.
Lightly moisten the palm of one hand with the hand water and rub your hands together. Take a small handful of rice (roughly ¼ cup (50g) and spread onto the left hand side of the nori. It should be 6mm thick.
Use your index finger to make a diagonal indentation and smear with wasabi if using.
Place the fillings in the indentation.
Bring the bottom corner of the nori into the middle, making a triangle. Roll the plain side around to make a cone and place it seam-side down.