Start by washing and trimming the green beans. Slice the chicken breast into thin strips and chop the garlic and ginger finely. If using bell peppers, slice them into thin strips as well.
In a bowl, combine the chicken strips with 2 tablespoons of soy sauce, 1 teaspoon of cornstarch, and a drizzle of sesame oil. Let it marinate for about 15-20 minutes while you prepare the rest of the ingredients.
In a large skillet or wok, heat 2 tablespoons of vegetable oil over medium-high heat. Ensure the pan is hot before adding the chicken.
Add the marinated chicken to the pan in a single layer. Allow it to cook undisturbed for about 3-4 minutes until it’s golden brown. Stir occasionally to cook evenly and then remove it from the pan.
In the same pan, add a bit more oil if necessary, then toss in the garlic, ginger, and green beans. Stir-fry for about 2-3 minutes. If using bell peppers, add them now and continue stir-frying for another 2 minutes.
Return the cooked chicken to the pan with the vegetables. Stir everything together, and add another tablespoon of soy sauce. Mix well to coat all ingredients.
If you want a thicker sauce, mix 1 tablespoon of cornstarch with 2 tablespoons of water to create a slurry. Pour it into the pan and stir quickly until the sauce thickens, about 1 minute.
Remove from heat and drizzle with additional sesame oil if desired. Serve your stir fry over rice or noodles for a complete meal!