• Step 1: In a large bowl, combine the sliced beef, soy sauce, brown sugar, and black pepper. Toss to coat the beef and let marinate for 15-30 minutes.
• Step 2: Heat the vegetable oil in a large skillet or wok over high heat. Working in batches if needed, add the marinated beef and cook for 2-3 minutes per side, until browned on the edges but still slightly pink in the center. Remove the beef from the skillet and set aside.
• Step 3: In the same skillet, add the sliced bell peppers, garlic, and ginger. Stir-fry for 2-3 minutes, until the peppers are starting to soften.
• Step 4: In a small bowl, whisk together the cornstarch and beef broth or water until smooth. Pour the cornstarch mixture into the skillet with the peppers and bring to a simmer, stirring constantly, until the sauce has thickened, about 1 minute.
• Step 5: Return the cooked beef to the skillet and toss everything together until the beef is heated through and coated in the sauce, about 2 minutes.
• Step 6: Remove from heat and stir in the sliced green onions. Serve immediately over cooked rice or noodles.