01 - Rinse rice under cold water until clear. Combine with water in pot or rice cooker, bring to boil, reduce heat, cover, and simmer 15 minutes. Remove from heat and let stand covered 10 minutes.
02 - In a medium bowl, combine beef with soy sauce, mirin, and cornstarch. Mix thoroughly and allow to marinate for at least 10 minutes.
03 - Combine soy sauce, oyster sauce, brown sugar, sesame oil, garlic, ginger, and broth in a small bowl. Stir to integrate and set aside.
04 - Heat oil in a large skillet or wok over medium-high heat. Add onions and carrots (if using) and sauté until slightly softened, about 2 to 3 minutes.
05 - Increase heat to high, add marinated beef, and stir-fry until browned, approximately 2 to 3 minutes.
06 - Pour prepared sauce over beef, cook for an additional 2 to 3 minutes stirring until sauce thickens and coats beef. Add green onions and toss briefly.
07 - Fluff rice and divide among bowls. Spoon beef mixture over rice. Garnish with reserved green onions and toasted sesame seeds if desired. Serve hot.