In a bowl, mix sliced beef with soy sauce and cornstarch. Let it marinate for 10 minutes.
Heat vegetable oil in a large pan or wok over medium-high heat.
Add beef and cook for 2-3 minutes until browned. Remove from the pan and set aside.
In the same pan, add bell pepper, broccoli, and carrot. Stir-fry for 3-4 minutes until slightly tender.
Add garlic and ginger, cooking for another 30 seconds until fragrant.
Return beef to the pan, then add beef broth, oyster sauce, hoisin sauce, sesame oil, and red pepper flakes. Stir well.
Cook for another 2 minutes until the sauce thickens and coats the beef and vegetables.
Serve hot over cooked rice and enjoy!