Heat 2 tablespoons of butter or cooking oil in a large skillet over medium heat. Sauté one diced onion until it becomes translucent, about 3-4 minutes. Add cooked chicken or your protein along with mixed vegetables. Stir for 2 more minutes. Incorporate day-old cooked rice, ketchup, soy sauce, and Worcestershire sauce, mixing well for about 2-3 minutes until combined.

Shape the fried rice mixture into a mound in the center of the skillet and let it sit for a moment to crisp up. Transfer to a plate and keep warm while preparing the omelet.

In a mixing bowl, whisk together 4 large eggs, 1 tablespoon of milk, salt, and pepper. Heat a non-stick frying pan over low heat, add a teaspoon of butter, then pour in the egg mixture and cook gently for about 3-4 minutes until the edges set but the center remains slightly runny.

Carefully slide the omelet onto the mound of fried rice on the plate. Tuck the edges of the omelet around the rice and drizzle ketchup over the top. Add chopped parsley or cheese if desired.

Serve immediately while warm, possibly pairing with miso soup or Japanese salad for a balanced meal.