01 - Toss the chicken slices with cornstarch, salt, and black pepper in a bowl until evenly coated.
02 - Heat vegetable oil in a large skillet or wok over medium-high heat. Add the chicken in a single layer. Cook for 2–3 minutes per side, until golden and cooked through. Remove chicken and set aside.
03 - Whisk together soy sauce, hoisin sauce, brown sugar, water, and cornstarch in a small bowl until smooth.
04 - Add a splash of oil to the same skillet if necessary, then add garlic and ginger. Sauté for 30 seconds until fragrant.
05 - Pour in the sauce mixture. Bring to a simmer and cook for 2–3 minutes, stirring frequently, until the sauce thickens.
06 - Return the chicken to the skillet and toss to coat in the sauce. Cook for 1–2 minutes more, until heated through. Stir in half of the sliced scallions. Serve immediately over steamed rice, garnished with remaining scallions and sesame seeds if desired.