Season the thin slices of steak generously with salt and pepper. Set aside.

In a large skillet, melt butter over medium heat. Add the onion and cook for 6 to 8 minutes, stirring occasionally, until the onion is lightly caramelized.

Next, toss in the sliced bell pepper and cook for another 3 to 4 minutes until the pepper softens. Season lightly with salt and pepper, then transfer the onion and pepper mixture to a separate plate.

Return the skillet to the stove, increase the heat to medium-high, and add the oil. Place the steak into the hot skillet and sear it for about 3 to 4 minutes until just cooked through.

Add the onion and pepper mixture back into the skillet with the steak and stir everything together until well combined.

Lay 3 slices of provolone on top of the mixture in the skillet. Pour 1-2 tablespoons of water along the edge of the pan and cover with a lid for about 1 minute, letting the cheese melt over the beef.

Once melted, give the mixture a stir. Add the remaining provolone slices on top, pour in another 2 tablespoons of water, and cover for 1 more minute to melt the cheese fully. Remove from heat.

Spread mayonnaise evenly on the hoagie rolls. Pile 1/3 of the cheesesteak mixture onto each roll. Serve immediately and enjoy!