Combine light soy sauce with dark soy sauce, oyster sauce, sugar, salt and pepper in a small bowl. Divide the sauce into two portions: scoop around 1 tablespoon of sauce as marinating sauce and half as stir-frying sauce.
Marinate the beef
Scoop around 1 tablespoon of the stir-fry sauce we prepared in the previous step. Use your hand to grasp the beef or mix until the meat absorbs the flavors. Then, add some extra water and cornstarch. Mix well until each of the beef slice is well coated by the marinating.
Add vegetable cooking oil to the beef and then mix well.
Fry the beef
Heat your wok or pan until very hot. Add cooking oil and fry minced garlic, ginger, and scallion white until aromatic. Spread the beef slices when the oil is warm but not hot. Let them stay for 3-5 seconds, then quickly fry them until they turn pale. Transfer out immediately.
Fry the shrimp
Leave the oil in the wok and add the shrimp. Fry for about half a minute until it changes color.
Mix them up
Add scallion sections and chopped Thai peppers. Return the beef and pour it into the bow sauce we prepared in the previous step. Quickly mix everything up.