Step 1: In a medium bowl, combine the chicken pieces with 1 tablespoon of soy sauce and 1 teaspoon of cornstarch. Toss to coat and set aside while you prepare other ingredients.
Step 2: In a small bowl, whisk together the chicken broth, 1/4 cup soy sauce, oyster sauce (if using), brown sugar, and sesame oil. In a separate very small bowl, whisk 1 tablespoon of cornstarch with 2 tablespoons of cold water to create a slurry. Set both aside.
Step 3: Heat 1/2 tablespoon of vegetable oil in a large wok or skillet over high heat until shimmering. Add the chicken in a single layer (cook in batches if necessary to avoid overcrowding) and sear for 2-3 minutes per side until lightly browned and cooked through. Remove chicken from the pan and set aside.
Step 4: Add the remaining 1/2 tablespoon of vegetable oil to the pan. Add the trimmed green beans and stir-fry for 3-5 minutes until tender-crisp. You can add a tablespoon of water and cover for a minute to steam them slightly if you prefer them softer.
Step 5: Add the minced garlic and grated ginger to the pan with the green beans. Stir-fry for 30 seconds until fragrant.
Step 6: Pour the prepared sauce mixture into the pan. Bring to a gentle simmer. Give the cornstarch slurry a quick whisk again and slowly pour it into the simmering sauce while stirring constantly. Cook for 1-2 minutes until the sauce thickens to your desired consistency.
Step 7: Return the cooked chicken to the pan and toss to coat evenly in the thickened sauce.
Step 8: Serve immediately over hot jasmine rice, garnished with sesame seeds and chopped green onions, if desired. Enjoy your homemade takeout!