Heat a large skillet over medium-high heat.
Add the lean ground beef to the skillet and cook, breaking it apart with a spatula, until browned and cooked through, about 6 to 8 minutes.
Drain any excess fat from the skillet.
Add the minced garlic and grated ginger to the beef and cook for 1 minute until fragrant.
In a small bowl, whisk together the soy sauce, brown sugar, sesame oil, crushed red pepper flakes, and black pepper.
Pour the sauce over the cooked beef in the skillet and stir to combine.
Cook for an additional 3 to 4 minutes, allowing the sauce to thicken slightly and coat the beef evenly.
Remove from heat and stir in the sliced green onions.
Transfer to a serving dish and sprinkle with toasted sesame seeds before serving.