In a bowl, combine the sliced steak with soy sauce and cornstarch. Let marinate for 15 minutes.
Heat 1 tbsp of oil in a large skillet over medium-high heat. Add the beef and cook until browned. Remove and set aside.
Add the remaining oil to the skillet. Sauté the bell peppers, onion, and garlic for about 3 minutes until slightly tender.
In a small bowl, mix beef broth, oyster sauce, brown sugar, and black pepper.
Return the beef to the skillet, pour in the sauce mixture, and stir well.
Simmer for 5 minutes until the sauce thickens.
Serve hot over cooked white rice.