To prepare the peas, plate it in a bowl and then blanch it in hot water. Leave it for 2 to 3 minutes, then discard the hot water and run the peas under cold tap water briefly. Shake off the excess water and set aside.
Put 1 tablespoon of butter into a frying pan over high heat. Add the chicken thighs and chopped onion and stir fry for 2 minutes.
When the onion becomes translucent and soften, add the mushrooms and ketchup and stir to combine well. Let it simmer to cook the chicken as well as thicken the sauce, for approximately 5 minutes.
Then add the boiled rice, and mix with a spatula in a sideway cutting motion. Add the green peas and adjust the seasoning with salt and pepper. Divide the rice into two portions and transfer each portion to a plate/bowl.
Get another frying pan onto the stove over medium heat.
Break 2 eggs into a small bowl, add a pinch of salt and pepper, then beat it slightly.
Add 1 tablespoon of butter onto the pan, and as it melts, add the eggs into it. Tilt the pan slightly and swirl the egg around, making sure it coats the entire base of the pan.
While the center of the omelette is still runny, place 1 portion of the rice in an oblong shape across the omelet on the center.
Transfer to a serving plate by placing a plate on top of the pan and then tipping the omelette and rice over. The omelette should be covering the rice which is resting on the plate now.
While the omelette on the plate is still warm, cover with a clean cloth and then tuck the omelette neatly to wrap around the rice. Adjust the shape till it forms a pillow shape.
Repeat Step 6 to Step 9 for the second serving of the Omurice.
Just before serving, squirt some ketchup on top of the Omurice and serve hot.