Marinate the chicken pieces in soy sauce, rice vinegar, hoisin sauce, oyster sauce, and cornstarch.
Let it stand for about 30 minutes.
In a small bowl, mix the soy sauce, rice vinegar, hoisin sauce, and oyster sauce for the stir-fry sauce.
Whisk until smooth.
Heat a large skillet over high heat with peanut oil.
Add the chicken and cook until browned on all sides, then transfer to a plate.
In the same skillet, add garlic, ginger, dried red chilies, and Sichuan peppercorn powder.
Cook for a minute or two until fragrant.
Add the bell pepper, scallions, and peanuts.
Toss in the chicken and stir-fry for another minute.
Serve hot over cooked rice or rice noodles.