In a mixing bowl, combine sliced beef with soy sauce, black pepper, and cornstarch. Let it marinate for about 10 minutes while you prepare the vegetables.

In a large pan or wok, heat the vegetable oil over medium-high heat until shimmering.

Add the marinated beef to the hot pan in a single layer. Sear both sides for about 2-3 minutes until they’re browned but not fully cooked through. Remove the beef from the pan and set it aside.

In the same pan, add sliced onion and bell pepper. Sauté for about 3-4 minutes, or until the vegetables start to soften.

Add the minced garlic to the vegetables and cook for another minute. Return the beef to the pan and toss everything together, cooking for an additional 2-3 minutes or until the beef is fully cooked.

Season with salt if needed and garnish with chopped green onions before serving.