Prep the Steak:
Freeze steak for about 30 minutes for easier slicing, then cut into thin strips.
Season with salt and pepper.
Cook the Veggies:
In a large skillet over medium heat, add olive oil.
Sauté onions (and peppers if using) for 5–7 minutes, until softened and slightly caramelized. Remove from skillet and set aside.
Cook the Steak:
In the same skillet, add steak slices in a single layer.
Cook over medium-high heat for 2–3 minutes, flipping halfway, until browned.
Return the onions and peppers to the pan and stir to combine.
Add the Cheese:
Place cheese slices over the meat and veggie mixture. Cover with a lid or foil and let melt for 1–2 minutes.
Assemble the Sandwiches:
Toast hoagie rolls if desired.
Spoon the cheesy steak mixture into each roll.
Serve hot with chips, pickles, or fries.