Prepare the chicken: Cut the chicken breasts or thighs into bite-sized pieces. Season them with salt and freshly ground black pepper. Set aside.

Make the sauce: In a small bowl, mix together the soy sauce, oyster sauce, rice vinegar, sesame oil, and chicken broth. Set this aside.

Stir-fry the chicken: Heat a large skillet or wok over medium-high heat. Add the vegetable oil and once hot, add the chicken pieces. Stir-fry until the chicken is golden brown and cooked through, about 5-7 minutes.

Add the aromatics: Add the minced garlic and grated ginger to the pan with the chicken. Stir-fry for another 1-2 minutes until fragrant.

Simmer with the sauce: Pour the prepared sauce mixture into the pan with the chicken. Stir to combine, making sure all the chicken is coated with the sauce. Let the sauce simmer for 3-4 minutes.

Thicken the sauce (optional): If you prefer a thicker sauce, mix the cornstarch with a small amount of water to form a slurry, then pour it into the pan. Stir and let it cook for another 1-2 minutes until the sauce thickens to your liking.

Serve: Remove from heat and garnish with fresh cilantro and sliced scallions if desired. Serve immediately over steamed rice or with your favorite side dish.