Slice up the vegetables you are using in the sandwiches. Put the cast iron skillet on the stove over medium-high heat and add compound butter to the skillet. Add the sliced vegetables. Stir occasionally.
While vegetables are cooking, slice the steak and butter the inside of the hoagie rolls.
Place the hoagie rolls under the oven broiler to toast. Watch closely so you don't burn the bread. I use the broiler on high, but every oven is different so low may be enough heat.
When the vegetables have started to brown and are softened, add the sliced steak to the pan. Stir to combine and immediately turn off the heat. Let the steak warm from the pan heat and vegetables.
Remove the hoagies from the oven, on the inside of the top put a thick layer of the cheese and on the bottom bun, pile the meat and veggies.
Place back under the broiler to melt the cheese and finish caramelizing the steak and vegetables.
Put the top and bottoms together when done, and enjoy.