Heat a large flat-top griddle or wok over medium-high heat with vegetable oil.

Sauté diced onions and carrots until tender, approximately 3 to 4 minutes.

Push vegetables to the side of the cooking surface, pour beaten eggs into the cleared space, and scramble until fully set.

Add the chilled rice and butter to the pan, using a spatula to break up any large clumps.

Drizzle soy sauce and sesame oil over the rice, then season with garlic powder and black pepper.

Stir-fry all components together for 3 to 5 minutes until the rice is heated through and develops a slightly crisp texture.

Fold in sliced green onions and serve immediately.