Cook 2 cups of short-grain Japanese rice according to package instructions, about 15-20 minutes, and let it cool.

In a large skillet, melt 1 tablespoon of butter over medium heat. Add 0.5 cup of chopped onion and 0.5 cup of chopped bell pepper, sauté for 4-5 minutes until soft.

Stir in 1 cup of diced cooked chicken and 0.5 cup of frozen peas, cook for another 3-4 minutes until heated through.

Reduce heat to low, stir in 2 tablespoons of ketchup and 2 tablespoons of soy sauce, add the cooled rice and mix until heated through, about 3-4 minutes.

In a large bowl, whisk together 4 eggs and 2 tablespoons of milk with a pinch of salt until smooth and frothy.

In a separate skillet, melt 1 tablespoon of butter over medium heat and pour in the egg mixture, cooking for 2-3 minutes until edges set.

Place a portion of rice filling in the center of the omelet when it's mostly set. Fold the sides over the filling.

Slide the omelet onto a plate, seam side down, and garnish with extra ketchup or sauce.