01 - Toss 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 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.
07 - Stir in half of the sliced scallions. Serve immediately over steamed rice, garnished with remaining scallions and sesame seeds if desired.