Heat the oil on a large griddle over medium-high heat and cook the mushrooms, bell pepper and onion with 1/4 teaspoon salt for 8 minutes until browned and dry.
Move the vegetables to one side and lay the salami strips on the open surface for 1 minute until their edges curl.
Add the shaved sirloin, season with the remaining salt and black pepper, and cook for 3 minutes until browned and at least 145°F.
Chop the steak lightly, then fold in the salami and vegetables until evenly distributed.
Divide the mixture into four piles, cover each with two provolone slices and let the cheese soften for 45 seconds.
Scrape the piles into the sub rolls and serve immediately while the mushroom edges are still crisp.