01 - Rinse rice under cold water until water runs clear. Combine with water in a saucepan, bring to a boil, reduce heat to low, cover, and simmer for 15 minutes. Remove from heat and let stand covered for 10 minutes.
02 - In a bowl, toss sliced beef with cornstarch, 1 tablespoon soy sauce, and sesame oil. Set aside to marinate while preparing remaining ingredients.
03 - In a small bowl, whisk together 1/4 cup soy sauce, mirin, brown sugar, oyster sauce, beef broth, and grated ginger. Set aside.
04 - Heat a large skillet or wok over medium-high heat. Add a splash of oil and sauté onions for 2 to 3 minutes until slightly softened. Add minced garlic and cook for 30 seconds.
05 - Push onions to the side and add beef in a single layer. Sear for 1 to 2 minutes per side until just browned.
06 - Pour sauce over beef and vegetables, tossing to combine. Simmer for 3 to 4 minutes until beef is cooked through and sauce thickens slightly. Stir in sliced green onions.
07 - Fluff steamed rice and divide among bowls. Top each portion with beef mixture and spoon additional sauce over top. Garnish with green onions, toasted sesame seeds, and pickled ginger as desired.