Mince the garlic and finely grate the ginger (or use a microplane). In a medium bowl combine soy sauce, rice wine (or sherry), sesame oil, minced garlic, grated ginger, cornstarch, and black pepper.

Add the chicken pieces to the marinade and toss to coat evenly. Cover and refrigerate for at least 20 minutes and up to 2 hours (short marination is fine because cornstarch will tenderize and give a glossy finish).

Sauce

While the chicken marinates, whisk together 1/2 cup chicken or vegetable stock, oyster sauce, hoisin sauce, dark soy (or extra light soy), brown sugar (or honey), and rice vinegar in a small bowl until sugar dissolves.

In a separate small cup, mix 1 teaspoon cornstarch with 1 tablespoon cold water to make a slurry; set aside.

Vegetables & Finish

Heat a large skillet or wok over medium-high heat until hot. Add 1 tablespoon of the vegetable oil and swirl to coat.

Remove chicken from the marinade, letting excess drip off. Add the chicken to the hot pan in a single layer (work in two batches if necessary) and spread out so pieces sear. Cook without moving for 2 minutes to get color, then stir-fry for another 2–3 minutes until external surface is golden and mostly cooked through. Transfer cooked chicken to a plate and keep warm.

Add the remaining 1 tablespoon vegetable oil to the pan. Slice the white and light-green parts of the scallions and add them with diced red bell pepper. Stir-fry 1–2 minutes until pepper begins to soften. Add the peas or snap peas and cook another 1 minute.

Return the chicken and any accumulated juices to the pan. Give the prepared sauce a quick stir and pour it over the chicken and vegetables. Stir to combine and bring the mixture to a simmer.

When the sauce is simmering, give the cornstarch slurry a quick stir and drizzle it into the pan while stirring constantly. Cook 1–2 minutes more until sauce thickens and becomes glossy, coating the chicken evenly.

Taste and adjust seasoning with up to 1/4 teaspoon additional salt or a splash more soy if needed. Stir in the dark green parts of the scallions and remove from heat.

Garnish with toasted sesame seeds and chopped cilantro if using. Serve immediately over cooked rice or noodles.