Prep the ingredients: cut the Boneless Skinless Chicken Thigh into bite-sized pieces, finely dice the Onion and Carrot, thaw the Frozen Green Peas if needed, and fluff the Cooked Japanese Short-Grain Rice so there are no large clumps.
Heat a large skillet over medium-high heat and add about 1–2 tablespoons of Neutral Oil. When hot, add the chicken and season with a pinch of Salt and freshly ground Black Pepper; cook until browned and mostly cooked through, about 4–5 minutes.
Add the diced onion and carrot to the skillet and sauté until softened, 3–4 minutes. Stir in the peas and cook for another 1–2 minutes so everything is heated through.
Push the vegetables and chicken to one side, add the rice and break up any remaining lumps. Fold everything together and stir-fry for 2–3 minutes until the rice is hot and well mixed.
Season the rice mixture by stirring in about 3–4 tablespoons of Ketchup and 1 teaspoon of Worcestershire Sauce (adjust to taste). Taste and add more Salt or Black Pepper if needed. Once evenly coated and heated through, transfer the ketchup rice to a plate and shape it into an oval mound.
In a bowl, beat 2–3 Eggs with 1–2 tablespoons of Milk and a light pinch of Salt and Black Pepper until just combined.
Wipe the skillet clean, melt about 1 tablespoon of Butter over medium-low heat, then pour in the beaten eggs. Swirl the pan and gently stir until the eggs begin to set but are still slightly runny on top—aim for a soft, custardy texture.
Slide the omelette onto the rice mound (folding the omelette over the rice or draping it on top), tuck the ends under to form a neat package, and brush or drizzle a little extra Ketchup on top for garnish. Serve immediately.
