Prepare the Chicken: In a large bowl, mix the chicken thighs with soy sauce, dark soy sauce, oyster sauce, black pepper, and corn starch. Let the chicken marinate for 10 minutes. While marinating, chop the scallions, separating the white parts from the green.
Pan-Fry the Chicken: Heat oil in a non-stick pan over medium heat. Add the marinated chicken pieces to the pan and pan-fry until they are fully cooked and golden on the outside.
Add Scallions: Once the chicken is cooked, add the white parts of the scallions to the pan. Cook until softened, stirring occasionally. If using larger chicken pieces or bone-in chicken, cover the pan with a lid and cook until the chicken is thoroughly cooked through. Finally, add the green parts of the scallions and stir for 10-20 seconds to lightly cook them.
Serve: Serve the scallion chicken warm, with a sprinkle of extra pepper or scallions on top if desired. Enjoy with steamed rice or noodles.