In a mixing bowl, combine the chicken strips with soy sauce, oyster sauce, and cornstarch. Mix well and let marinate for at least 20 minutes in the refrigerator.

Heat a wok or large frying pan over medium-high heat and add 2 tablespoons of vegetable oil.

Add garlic and ginger to the pan, stir-frying for about 30 seconds until fragrant but not letting them brown.

Increase heat to high. Add the marinated chicken to the wok, cooking until well-browned and cooked through, about 5-6 minutes. Remove chicken and set aside.

In the same wok, add the remaining 2 tablespoons of vegetable oil. Add onion, red bell pepper, and green bell pepper, stir-frying for about 3 minutes until vegetables are slightly tender.

Return the chicken to the wok and stir everything together. Add light soy sauce, dark soy sauce, and rice wine or dry sherry. Stir-fry for another 2 minutes until well combined.

Drizzle with sesame oil and sprinkle with chopped spring onions. Season with salt and pepper to taste.

Serve hot, ideally with steamed rice or noodles.