Cut the chicken thigh into bite-sized pieces.

Slice the onion thinly and trim the mushroom stems before slicing them.

Mix the ketchup rice ingredients in a bowl and spread them into a heatproof dish.

Heat salad oil in a pan and cook the chicken, skin-side down, until browned on both sides.

Add the onion and mushrooms to the pan and sauté for about 3 minutes until the onion softens. Add butter and mix well.

Sprinkle flour into the pan and stir until no longer powdery. Gradually add milk and cook until the mixture thickens.

Season with salt and pepper, then pour the mixture over the ketchup rice.