In a large skillet, heat the oil with the onions, Saute on medium low heat until they become soft and translucent.
Once the onions are sautéed, add in the mushrooms and season with salt. This helps bring the moisture out of them to become soft as well as seasons them.
Once the mushrooms are soft, add in the shaved steak along with 2-3 tablespoons of your favorite steak seasoning.
Cook the steak until it's cooked through, about 8-10 minutes. Toss the steak around in the onions and mushrooms.
Spread mayo on the hoagie buns then place steak on the bottom roll and the provolone cheese on the top.
Place in the air fryer at 350°F (or in the oven) to toast the bread and melt the cheese. In the air fryer it'll take about 1-2 minutes and about 5-8 in the oven.
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Notes
Add the Onions and Peppers: Cooking onions and peppers slowly brings out their natural sweetness and adds rich depth to the sandwich. Let them soften over low heat for the best flavor.
Salt the Mushrooms Early: A sprinkle of salt helps release the mushrooms' moisture, making them tender and enhancing their savory taste as they cook.
Finish with Melty Cheese: After building the sandwich, use your air fryer or broiler to melt the cheese and give the bread a lightly toasted finish—it only takes a couple of minutes
Reheating Tips: Wrap the sandwich in aluminum foil to keep the sandwich from drying out and air fry (or bake) at 350°F for 5-8 minutes depending on how thick the sandwich is.