Whisk the sauce: In a small bowl, mix soy sauce, brown sugar, gochugaru, rice vinegar, and sesame oil.
If you want a thicker glaze, whisk in cornstarch until smooth. Set aside.
Prep aromatics: Mince the garlic and ginger, and slice the green onions. Keep the whites and greens separated for cooking and garnish.
Cook the beef: Heat a large skillet over medium-high heat.
Add oil if your beef is very lean. Add ground beef and break it up with a spatula. Cook until browned with crisp edges, about 5–7 minutes.
Drain excess fat if needed for a cleaner sauce.
Add aromatics: Reduce heat to medium. Stir in garlic, ginger, and the white parts of the green onions. Cook 30–60 seconds until fragrant.
Don’t let the garlic burn.
Sauce it up: Pour in the sauce and toss to coat the beef. Simmer 2–3 minutes until it thickens slightly and clings to the meat. Taste and adjust heat or sweetness as needed.
Add veggies (optional): If using quick-cook vegetables, stir them in now and cook 1–2 minutes until just tender but still crisp.
For firmer veggies like broccoli, steam or sauté separately and fold in at the end.
Finish and serve: Remove from heat. Sprinkle with sesame seeds and the green onion tops. Serve over hot rice, and spoon extra sauce from the pan over each bowl.