Preheat your oven to 350°F and line a baking sheet with parchment paper.
Chop everything up. Dice the roast beef, green pepper, onion, and mushrooms into small pieces so they fit nicely inside the tiny phyllo shells.
Heat a skillet over medium heat. Toss in the green pepper and onion, cooking for about 5 minutes until they start to soften up nicely.
Add the roast beef, mushrooms, and steakhouse seasoning to the pan. Cook for another 5 minutes, stirring everything together so the flavors get to know each other.
Stir in half of the shredded provolone and let it melt right into the warm meat and veggie mixture.
Spoon the savory cheesesteak mixture into the phyllo shells. Top each one with a little bit of the remaining cheese.
Arrange the filled shells on your prepared baking sheet and bake for about 10 minutes, just until the cheese is melted and the phyllo shells are warmed through.
Remove from the oven, let them cool for just a minute so you don't burn your mouth, and serve warm.
