In a bowl, combine the sliced chicken with 1 teaspoon baking soda, 1 tablespoon cornstarch, 1 tablespoon water, 1 tablespoon soy sauce, and 1 tablespoon sesame oil. Mix to coat and let marinate for 15–20 minutes.
Rinse the marinated chicken under cold water to remove the baking soda, then pat the pieces dry with paper towels.
In a small bowl, whisk together 3 tablespoons soy sauce, 1 tablespoon oyster sauce, 1 tablespoon hoisin sauce, 1 tablespoon rice vinegar, and 1 teaspoon cornstarch (if using). Set the sauce aside.
Heat 1 tablespoon sesame oil in a wok or large skillet over medium-high heat. Add the chicken, season lightly with salt and pepper, and stir-fry for 5–6 minutes until cooked through and lightly browned. Remove the chicken and set aside.
Add the remaining 1 tablespoon sesame oil to the same skillet. Sauté the minced garlic and minced ginger for about 1 minute until fragrant.
Add the frozen green beans and stir-fry for 4–5 minutes until heated through and slightly tender.
Return the cooked chicken to the skillet, pour the prepared sauce over the chicken and beans, and stir to coat. Cook for another 2 minutes until heated through and the sauce slightly thickens.
Transfer to a serving dish and garnish with sliced green onions and sesame seeds before serving.