1Slice the flank steak into thin strips.
In a large skillet, heat the olive oil over medium-high heat.
Add the sliced steak to the skillet and cook until browned, about 5-7 minutes.
Remove the steak from the skillet and set aside.
In the same skillet, add the sliced green bell pepper, red bell pepper, and onion. Cook until they start to soften, about 5 minutes.
Add the minced garlic and sliced mushrooms to the skillet. Cook for an additional 2-3 minutes.
In a small bowl, mix the beef broth, soy sauce, and cornstarch until well combined.
Return the steak to the skillet and pour the broth mixture over the steak and vegetables.
Stir well and cook until the sauce thickens, about 3-5 minutes.
Season with black pepper to taste.
Serve hot and enjoy your Pepper Steak with Mushrooms.