Prepare the peppers and onions: In a nonstick skillet over medium heat, melt the butter. Add the sliced onions, green and orange bell peppers. Saute until they turn golden and soft, about 5-7 minutes. Transfer the cooked vegetables to a covered bowl and set aside in the microwave to keep warm.
Cook the beef: In the same skillet, add the beef strips. Stir-fry over medium-high heat until browned but still tender, around 4-5 minutes. Avoid overcooking. Season with salt and freshly ground black pepper.
Tips:If you want, you can lightly toast the hoagie buns with a bit of butter before assembling.Use your choice of cheese: provolone gives a classic taste, while mozzarella provides a creamier texture.