Prep the Oven: Preheat your oven to 375°F (190°C).
Sauté the Steak: In a large skillet, heat the olive oil over medium heat. Add the thinly sliced steak and cook until browned, stirring occasionally.
Cook the Veggies: Add in the sliced onion, green bell pepper, and mushrooms to the skillet, cooking until the vegetables are tender. Season with salt and pepper to your liking.
Layer the Casserole: In a greased baking dish, start by layering the frozen hash browns. Follow that with the steak and vegetable mixture spread evenly across the top.
Add Broth: Pour the beef broth evenly over the layered ingredients, allowing it to soak in.
Cheesy Goodness: Sprinkle the provolone and mozzarella cheese generously over the top.
Bake: Cover the dish with aluminum foil and bake for 30 minutes. Then, remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden brown.
Cool and Serve: Let it cool for a few minutes before serving – this will help the casserole set a bit for easier slicing!