In a large mixing bowl, whisk together soy sauce, rice vinegar, sesame oil, and cornstarch until combined. Add the chicken breasts and coat well. Cover and marinate for at least 15 minutes.

While marinating, chop scallion tops and mince garlic and ginger.

Heat the vegetable oil in a skillet over medium-high heat until shimmering.

Add the marinated chicken; cook for 5-7 minutes per side until golden brown and cooked through.

Reduce heat; add minced garlic, ginger, and scallion whites to the skillet. Sauté for 2-3 minutes.

Pour in the remaining marinade, simmer for 2-3 minutes until it thickens slightly.

Remove from heat, let rest, slice, and serve over rice or noodles drizzled with remaining sauce.