Slice steak against the grain into 2" pieces about 1/4" thick. Place in a bowl and add baking soda, light soy sauce, sesame oil, white pepper, cornstarch, and avocado oil. Mix well and marinate for 20 minutes.
Mince garlic and slice onions and bell peppers and set them aside with the beef.
In a small bowl, mix together oyster sauce, shaoxing wine, light soy sauce, dark soy sauce, coarse black pepper, sugar, beef stock, msg (optional), and cornstarch. Mix until the sauce is thoroughly combined.
Heat 4 tbsp of oil in a large wok or pan over high heat and cook the beef (in batches if needed) for 2-3 minutes until golden brown. Remove the beef and leave about 2 tbsp of oil in the pan.
Over medium high heat, add the minced garlic and saute for 30 seconds. Add the sliced onions and bell pepper and cook for 1-2 minutes over high heat or until the vegetables are slightly softened but still crisp.
Add the cooked beef back to the pan. Mix the sauce a final time to pick up any cornstarch, then pour the sauce along the edge of the wok or pan.
Mix and toss the sauce and ingredients for another 1-2 minutes over high heat until the sauce has thickened. Serve with white rice and enjoy!
Notes
Slice Steak Against the Grain: Follow the lines (which is the muscle fibers) in the raw steak and cut against them. Slicing beef against the grain is an easy way to get tender Black Pepper Beef - cutting the fibers of the muscle means they won't get tough when cooked.Cut the Vegetables to Similar Sizes: I always recommend cutting your vegetables into similar sized pieces so they cook evenly - this little step makes a huge difference! In this recipe for Black Pepper Beef, I cut the bell peppers and onions in to similar sizes so they would cook evenly!Success is in the Prep: Once you start cooking, Black Pepper Beef will come together very quickly. The key to pulling this off successfully is having all of your ingredients prepped and in bowls right next to your wok or pan (like in the photo shown below)! Have your premixed sauce, beef, and vegetables ready and easily accessible during the cooking process. Make sure to stir the cornstarch slurry one more time before adding it into the wok or pan.
Storage and Reheating Tips
You can store leftover Black Pepper Beef in the refrigerator in an airtight container for up to 3 days.Because Black Pepper Beef is not coated in a batter, you won't have to worry about trying to restore the crispy texture of the dish - I recommend reheating this in the microwave or in a hot pan/wok for a couple minutes (add a little bit of water if you want to loosen up the chicken pieces that stuck together in the refrigerator).