In a bowl, combine the sliced chicken breasts with baking soda, cornstarch, water, soy sauce, and sesame oil. Mix until the chicken is fully coated. Let it marinate for 15-20 minutes. Velveting helps tenderize the chicken and gives it a silky texture.
After marinating, rinse the chicken under cold water to remove the baking soda. Pat the chicken dry with paper towels.
In a small bowl, whisk together the soy sauce, oyster sauce, hoisin sauce, rice vinegar, and cornstarch (if using). Set aside.
Heat 1 tablespoon of sesame oil in a large skillet or wok over medium-high heat. Add the sliced chicken and season with a little salt and pepper. Stir-fry the chicken for 5-6 minutes, until fully cooked and lightly browned. Remove the chicken from the skillet and set aside.
In the same skillet, add the remaining tablespoon of sesame oil. Add the minced garlic and fresh ginger, and sauté for about 1 minute until fragrant. Add the frozen green beans directly to the skillet and stir-fry for 4-5 minutes until they are heated through and slightly tender.
Return the cooked chicken to the skillet with the green beans. Pour the sauce over the chicken and beans, stirring to coat everything evenly. Let it cook for another 2 minutes to heat through and slightly thicken.
Transfer the stir fry to a serving dish. Garnish with sliced green onions and a sprinkle of sesame seeds.
