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

Take your chicken and slice it into thin strips, ensuring even cooking. Combine the chicken with the prepared marinade, cover, and let it marinate for at least 20 minutes.

Place a large skillet over medium-high heat and add a light drizzle of oil. Heat for about 2-3 minutes until shimmering.

Add the marinated chicken to the hot skillet in a single layer. Cook for 5-7 minutes, turning occasionally until the chicken is browned and cooked through.

Transfer the chicken to a serving plate. Garnish with toasted sesame seeds and extra chopped green onions, serve with rice or lettuce for wraps.