Heat a large skillet over medium heat and melt 2 tablespoons of butter. Add diced chicken and sauté for about 5-7 minutes until golden brown and cooked through. Stir in finely chopped vegetables and cook until tender, about 3 minutes. Next, add cooked rice and 3 tablespoons of ketchup, mixing well to combine. Cook for another 2-3 minutes until heated through; set aside to cool slightly.

In a bowl, whisk together 4 eggs with a pinch of salt and pepper until well combined. Heat a non-stick frying pan over low heat and add 1 tablespoon of butter. Pour in the egg mixture and gently stir with a spatula, allowing the edges to set while the center remains slightly runny, about 2-3 minutes.

Once the omelette is cooked but still soft in the center, place a generous portion of the chicken rice mixture in the center. Fold the omelette gently over the rice, creating a neat package. Allow it to cook for an additional 1-2 minutes.

To plate your Omurice, carefully slide the wrapped omelette onto a warm plate, seam side down. Drizzle with extra ketchup or your favorite sauce. Garnish, if desired, and enjoy!