Preheat the oven to 350F.

In a large oven-safe skillet, heat half of the olive oil over medium-high heat.

Add the thinly sliced beef; season with salt and pepper to taste and saute until browned. Remove from the pan and set aside.

Add the onion and bell peppers to the skillet, season with salt and pepper, and cook for 3-5 minutes, until softened. Add the garlic and cook for 30-60 seconds.

Add the beef broth and Worcestershire sauce and stir. Return the beef to the pan, then layer the American cheese on top of everything. Cover the pan and simmer, allowing the cheese to melt, then remove the lid and stir it into the beef and veggies. Reduce the heat to medium and allow it to simmer down a bit, until the sauce thickens.

Sprinkle the top with chopped tomatoes, then sprinkle or layer on the provolone cheese. You can also transfer the mixture to a casserole dish at this point.

Bake for 10-15 minutes, or until the cheese is melted and the casserole is heated through. Broil for 2-3 minutes for a golden brown top.