1. Begin by combining the soy sauce, rice vinegar, sesame oil, and cornstarch in a bowl. Add the chicken breasts and ensure they are evenly coated with the marinade. Cover and let the chicken marinate for at least 15 minutes.

2. While the chicken is marinating, chop the scallions and mince the garlic and ginger.

3. In a large skillet or wok, heat the vegetable oil over medium-high heat.

4. Once the oil is hot, add the marinated chicken breasts to the skillet. Cook for approximately 5-7 minutes on each side, or until the chicken is golden brown and cooked through, with an internal temperature reaching 165°F.

5. When the chicken is cooked, add the minced garlic, ginger, and chopped scallions to the skillet. Sauté for 2-3 minutes.

6. If there is any leftover marinade in the bowl, pour it into the skillet. Let the sauce simmer for a few minutes to thicken slightly.

7. Remove the skillet from the heat and let the Chinese Scallion Chicken rest for a minute. Slice the chicken and serve it alongside rice or noodles, drizzling the sauce over the top.