In a large skillet over medium heat, add the butter and oil.
Sauté the onions and green peppers until soft and golden, about 5–7 minutes.
Push the veggies to one side of the pan, then add the beef. Season with salt and pepper.
Cook the beef until browned and tender, about 4–5 minutes, stirring occasionally.
Mix the onions and peppers back in with the beef.
Top the mixture with provolone slices and let it melt over everything.
Spoon the cheesy beef mixture into toasted hoagie rolls and serve hot.