In a medium bowl, whisk together soy sauce, brown sugar, minced garlic, grated ginger, and sesame oil until the sugar dissolves. Stir in chopped green onions and black pepper.

Slice chicken into thin strips and toss in the marinade, covering well. Refrigerate for at least 20 minutes or up to 2 hours.

Heat a large skillet over medium-high heat, add oil, and cook the marinated chicken in a single layer for 5-7 minutes until cooked through.

Transfer Chicken Bulgogi to a serving plate, sprinkle with sesame seeds and green onions. Serve warm alongside rice or side dishes.