Prepare the Ingredients: In a large skillet, heat the olive oil over medium-high heat. Add the thinly sliced beef, season with salt and pepper, and cook for 3-4 minutes until the beef is just browned.
Sauté the Vegetables: In the same skillet, add the sliced onion, bell pepper, and minced garlic. Continue cooking for approximatively 3-4 minutes until the vegetables are softened and fragrant. Remove from heat.
Layer in the Crockpot: In the bottom of your crockpot, add the diced potatoes, spreading them out evenly. Season with salt, pepper, dried oregano, and dried basil. Pour the sautéed onion, bell pepper, and garlic mixture over the potatoes.
Add the Beef and Broth: Place the browned beef slices on top of the vegetables. Pour the beef broth over the mixture to add moisture and enhance the flavors.
Cook in the Crockpot: Cover and cook on low for 6-7 hours or on high for 3-4 hours, until the potatoes are tender and the flavors have melded together.
Add the Cheese: About 30 minutes before serving, sprinkle the shredded provolone (or Swiss) and cheddar cheese evenly over the top of the casserole. Cover and let the cheese melt completely into the dish.
Serve: Once the cheese is melted and bubbly, the casserole is ready to serve. Garnish with additional fresh herbs, if desired, and enjoy this warm, comforting dish with a side salad or crusty bread.