Preheat your oven to 350°F and line a baking sheet with parchment paper for easy cleanup.

Dice the roast beef, green pepper, onion, and mushrooms into small, even pieces.

Place a skillet over medium heat, then add the chopped green pepper and onion. Cook for about 5 minutes, stirring occasionally, until they start to soften.

Add the roast beef, mushrooms, and steak seasoning. Continue cooking for another 5 minutes, letting the flavors blend together.

Spoon the mixture into the phyllo shells, filling each one evenly. Sprinkle a little extra cheese on top of each cup.

Place the filled shells on the prepared baking sheet and bake for about 10 minutes, or until the cheese is melted and the shells are crisp.

Let them cool for a minute or two, then serve warm and enjoy!