Chop chicken into 2cm chunks and combine in a bowl with soy sauce and mirin. Allow to marinate in the refrigerator for 1 hour. Heat a frying pan or grill and cook chicken in a little oil until completely cooked through. Mix cornflour with a small amount of water and then stir through the chicken. Allow chicken to cool until completely cold.

Place a nori sheet on a sushi rolling mat with the rough side up. Place a quarter of the sushi rice over half of the nori mat. In the centre of the rice make a line of chicken and wasabi if desired. Lift the mat at the end closest to you and start to roll the sushi pressing the filling as you go to ensure the rolls are tight. Once you get to the end wet the edge with a little water to seal and then slice into 6 pieces.