Marinate the chicken according to our velvet chicken recipe (see Note 1). Mix in 1 teaspoon ground black pepper. Set this aside while you prepare the other ingredients. Mix together the ingredients for the black pepper sauce: ⅓ cup water, 1 tablespoon oyster sauce, ½ tablespoon light soy sauce, 2 teaspoons dark soy sauce, 1 teaspoon sugar, 1 teaspoon ground black pepper, and 1 teaspoon cornstarch. Set aside.
Heat half of 2 tablespoons oil in a wok or sauté pan on medium-high heat. Spread 8 to 10 ounces velvet chicken breast over the wok in a single layer. Sear for a minute or two until golden brown, then flip and sear the other side. The chicken pieces should release easily from the pan with a thin metal spatula.
Transfer the chicken to a plate. Don’t worry about the middle being undercooked, we’ll be heating it through later.
Return the wok to the heat and add the remaining half of 2 tablespoons oil. Throw in 1 small onion and ½ sliced bell pepper. Cook until fragrant and the edges are starting to brown.
Add 6 cloves garlic and stir fry for another 20 seconds or so. Be careful not to burn it. Deglaze with 2 teaspoons Shaoxing wine, if using.
Pour in the black pepper sauce from step 2. Bring it to a simmer, then add back the chicken. Stir to coat in black pepper sauce, until sauce is slightly thickened and clinging to the chicken. Remove from heat and top with 1 to 2 scallions.