In a mixing bowl, mix together Chicken, Light Soy Sauce, Garlic, Egg White, and Cornstarch. Set aside for later.
Roast the Sichuan Peppercorns and Black Peppercorns in a frying pan over medium-high heat for 1-2 minutes. Transfer to a mortar and grind into fine powder.
Make the Pepper Sauce. In a bowl, add in 1.5 tbsp of the Pepper mix, Oyster Sauce, Chinese Cooking Wine, and Dark Soy Sauce. Mix well and set aside.
In a wok or frying pan, on medium-high heat, add in Vegetable Oil. Once the Oil is ready, add in the Chicken pieces one at a time. Fry the Chicken in batches. Fry the Chicken for 3-4 minutes until golden. Drain and repeat the process.
In a wok, add in Vegetable Oil over medium-high heat. Add in Garlic and stir for 10 seconds until fragrant. Then add in the Onion and the Bell Peppers. Stir fry for 1-2 minutes. Add in the Chicken and the Pepper Sauce. Mix well.
Turn off the heat. Add in Green Onions. Combine everything well. Transfer to a plate and ready to serve!