01 - In a large mixing bowl, whisk together the soy sauce, brown sugar, sesame oil, minced garlic, grated ginger, rice vinegar, gochugaru, and black pepper until the sugar dissolves and the mixture is well blended.
02 - Add the thinly sliced beef to the marinade and toss thoroughly to ensure every piece is evenly coated. Allow the beef to marinate for at least 10 minutes at room temperature, or up to 1 hour in the refrigerator for deeper flavor penetration.
03 - Heat a large skillet or wok over high heat until it begins to smoke. Add the marinated beef in a single layer and cook for 3 to 4 minutes, stirring occasionally, until the beef is deeply browned and cooked through.
04 - Remove the skillet from heat and fold in half of the sliced green onions and 1 teaspoon of the toasted sesame seeds, reserving the remainder for garnish.
05 - Mound steamed white rice onto plates or bowls, spoon the hot beef and sauce over the rice, and finish with the remaining green onions and sesame seeds. Serve immediately.