Begin by slicing the chicken breast into thin strips, chop the bell peppers and onions, and mince the garlic and ginger.

Combine the sliced chicken with soy sauce, cornstarch, and black pepper in a mixing bowl and allow to marinate for about 10 minutes.

Heat a wok or large pan over medium-high heat, add vegetable oil, and stir-fry the onions and bell peppers for 3-4 minutes.

In the same wok, add more oil if needed, then add the marinated chicken in a single layer and cook for 3 minutes undisturbed.

Stir-fry the chicken for another 2-3 minutes until fully cooked.

Return the sautéed vegetables to the wok with the chicken, add minced garlic, ginger, soy sauce, oyster sauce, and adjust black pepper.

Toss everything together for 1-2 minutes, then garnish with sliced green onions and serve immediately.