Cut the chicken breast into bite-sized pieces.
Slice the onion.
Add cooking oil to a pan and stir-fry the chicken breast.
When the chicken is halfway cooked, add the onion and stir-fry together.
Add a little soy sauce, mirin, and sugar, then simmer.
Place the chicken breast and onion on top of the rice.
Sprinkle green onions and seaweed flakes as desired.