In a small bowl, combine the soy sauce, oyster sauce, Chinese cooking wine, cornstarch, white pepper, salt, and sugar. Stir well until the cornstarch is dissolved and set aside.

Place the sliced pork in a medium bowl. Pour half of the prepared sauce over the pork and mix gently to coat the strips evenly. Let it marinate for 10 - 15 minutes.

Heat a wok or large frying pan over high heat. Add 1 - 2 tablespoons of vegetable oil. When the oil is hot (it should shimmer), add the marinated pork strips in a single layer. Cook for 2 - 3 minutes until the pork is almost cooked through and starts to brown, stirring occasionally. Remove the pork from the wok and set aside.

Add another tablespoon of vegetable oil to the same wok if needed. Add the minced garlic, grated ginger, and dried red chilies (if using). Stir - fry for about 30 seconds until fragrant.

Add the sliced green peppers to the wok. Stir - fry for 3 - 4 minutes until the peppers start to soften but still retain a bit of crunch.

Return the cooked pork to the wok. Pour in the remaining sauce and add the sliced green onions. Stir - fry everything together for 1 - 2 minutes, until the sauce thickens and coats the pork and peppers evenly.