Melt the butter in a large frying pan over medium heat, then add the onions and cook until they soften and brown – about 10 minutes.
Add the chicken and mushrooms, and cook for another five to 10 minutes, until these brown as well.
Pour in the stock, soy, mirin and sugar, and cook for 10 minutes, or until the liquid reduces and coats the chicken.
Lower the heat and crack in the eggs. Break the yolks and stir gently. When cooked to a semi-scrambled consistency, take off the heat.
Scoop the rice into deep bowls, top with the chicken and egg mixture, and garnish with spring onions and chilli powder.
