Add chicken to a saucepan and saute over medium heat for 5 minutes.
Add onion and cook until soft.
Add enough stock to cover the meat.
Add soy sauce, mirin and sugar to the saucepan.
Bring to the boil and then simmer until slightly reduced.
Whisk the eggs in a bowl.
Pour the eggs over the chicken and onion.
Turn the heat to low and cover with a lid.
Once egg is cooked turn off heat.
To serve spoon cooked rice of your choice into a deep bowl. I prefer to use Jasmin or basmati rice over sticky Japanese rice. Place the chicken mixture on top of the rice and spoon some of the stock mixture on top.