Preheat the oven to 425° F.
Place the sliced peppers, onions, and mushrooms on a sheet pan covered in foil or parchment paper for easier cleanup. Place the salmon on the sheet pan, skin side down. Drizzle everything with olive oil and season with your favorite steak seasoning.
Roast in the oven for 15 - 18 minutes, turning the veggies once during the roasting process.
Meanwhile, slice the hoagie rolls in half, butter the inside generously, and place the buttered side down on a separate sheet pan. Place the rolls in the oven when there are just a few minutes left for the salmon (12-minute mark) and toast the rolls for 2-3 minutes until golden brown. Remove the rolls from the oven and turn over so the buttered, toasted side is facing up. Place 2 slices of provolone cheese on the bread and place back in the oven for another minute or so until the cheese is melted.
Remove the salmon, veggies, and cheese bread from the oven. Flake the salmon with a fork. Place the salmon onto the cheesy bread, then top with the roasted peppers, mushrooms, and onions.