First, cut your beef into thin slices.
Marinate it with 1 tbsp of light soy sauce and 1 tbsp of Chinese cooking wine, you can use regular rice wine too. Some freshly ground pepper, 1/4 tsp of baking soda, 1.5 tsp of corn starch
Set your beef aside for at least 30 minutes. While waiting we can make the sauce.
1 tbsp of oyster sauce, 1 tbsp of light soy sauce, 1/4 cup of water, 1 tsp of corn starch, 1 tsp of sugar, 1 tsp of freshly ground black pepper and some salt to taste. Because soy sauce already has a lot of sodium, don’t put a lot. Just a little pinch should be fine.
For the vegetables, I prepared some green and red pepper cut into big chunks. Some onion and 1 tbsp of minced garlic.
Heat up your wok on the highest level possible for 10 seconds and add about 1 tbsp of vegetable oil. Add in your beef. Let the beef fry for 15-20 seconds on each side. Keep turning IT every 15 seconds until the beef becomes brown. Take it out and set it aside.
Add about 1 tbsp more oil into the same wok and throw in all your vegetables. Stir fry this for about 2 minutes.
When you see the onion becoming transparent turn the heat to low. Add the beef back into the wok along with the sauce. Mix it quickly. Soon you will see the sauce getting thicker. Turn it off. Take it out and you are done.