Marinate beef strips with beef marinade ingredients for at least 5 minutes.

In a small bowl, combine all the sauce ingredients and mix well.

Heat 1 tablespoon of oil in a non-stick pan over medium heat. Add marinated beef strips and stir-fry for about 3 minutes until browned on all sides.

Remove beef from the pan and set aside.

Using the remaining oil in the pan (add a little more if needed), add sliced onions and bell peppers. Stir-fry for about 3 minutes until they start to soften.

Lower the heat slightly, then return the beef to the pan with the vegetables. Mix the sauce again, then pour it all over the beef and vegetables. Let the sauce simmer for about 30 seconds, or until it starts to thicken. Stir until everything is evenly coated with the sauce.

Plate the Black Pepper Beef Stir Fry and garnish with some chopped green onions. For a spicy kick, you can add some crushed red pepper flakes or chili oil. Serve with a side of steamed rice for a complete meal. Enjoy!