Begin by preparing your ingredients: thinly slice the ribeye steak, bell peppers, onion, and mushrooms.
In a bowl, mix the sliced steak with olive oil, garlic powder, salt, and pepper, ensuring the steak is evenly coated.
Lay out the aluminum foil sheets and evenly divide the steak, bell peppers, onions, and mushrooms between them.
Fold the foil over the ingredients, sealing the edges to create individual packets.
Cook the foil packets on a grill over the campfire or directly on the embers for about 10 minutes on each side, being careful when flipping to avoid tearing.
Open the foil packets and sprinkle shredded provolone cheese over the contents. Seal the packets back up and return them to the fire for an additional 2-3 minutes, or until the cheese has melted.
Serve the Philly Cheesesteak Foil Packets hot, directly from the foil, and enjoy a hearty, flavorful meal by the campfire.