Cook the rice according to package instructions or reheat day-old rice for about 15 minutes until fluffy.

Dice the red, yellow, and green bell peppers, finely chop the onion, and mince the garlic.

Heat 1 tablespoon of vegetable oil in a large skillet over medium-high heat. Add ground beef and cook for 5–7 minutes until browned.

Add finely chopped onion and minced garlic to the skillet and sauté for 1–2 minutes until onion is translucent.

Toss diced bell peppers into the skillet and stir-fry for 3–4 minutes until the peppers are tender but still crisp.

In a small bowl, combine soy sauce, oyster sauce, brown sugar, and ground black pepper. Stir until sugar is dissolved, and add sesame oil if desired.

Pour sauce into the skillet, stirring to coat beef and vegetables, and let simmer for 2-3 minutes.

Add cooked rice to the skillet, mixing thoroughly until heated through and well combined.

Garnish with chopped green onions or sesame seeds if desired, and serve hot.