In a mixing bowl, combine soy sauce, brown sugar, sesame oil, minced garlic, and black pepper. Whisk until well blended.
Add the sliced chicken to the marinade, ensuring each piece is well coated. Cover and refrigerate for at least 15 minutes (or up to overnight for deeper flavor).
Heat a large skillet or grill pan over medium-high heat. Add a little oil if needed to prevent sticking.
Once the pan is hot, add the marinated chicken in a single layer. Cook for about 5-7 minutes, stirring occasionally, until the chicken is browned and cooked through.
Once cooked, remove the chicken from heat and garnish with chopped green onions.
Transfer the chicken to a serving dish, allowing guests to help themselves.
Notes
Adjust the marinating time based on your preference for flavor intensity.