In a bowl, combine sliced chicken, soy sauce, cornstarch, and vegetable oil. Mix well and let it marinate for 10 minutes.

Heat a wok over medium-high heat and add 1 tablespoon of vegetable oil. Add the marinated chicken and stir-fry until cooked through, about 5-7 minutes. Remove from the wok and set aside.

In the same wok, add garlic and chilies. Stir-fry for about 30 seconds until fragrant.

Add sliced bell pepper and stir-fry for another 2-3 minutes until slightly tender.

Return the cooked chicken to the wok. Add soy sauce, oyster sauce, fish sauce, and sugar. Stir well to combine and cook for an additional 2 minutes.

Add Thai basil leaves and stir until wilted. Serve hot over rice.