Bring a large pot of salted water to a boil and cook the 1 pound tortellini according to the package directions. Drain and set aside.
While the water heats, pat the 1½ pounds sliced steak dry and season with the ½ teaspoon salt and ½ teaspoon black pepper. Heat the 2 tablespoons olive oil in a large skillet over high heat and sear the steak in a single layer for 2 to 3 minutes, just until browned. Work in batches if you need to, since crowding the pan steams the meat instead of searing it. Transfer the steak to a plate.
Lower the heat to medium and add the 1 tablespoon butter to the same skillet. Add the sliced onion, bell pepper, and mushrooms and cook for 6 to 7 minutes, until softened and starting to caramelize. Stir in the 3 cloves minced garlic and cook for 1 minute more.
Sprinkle the 2 tablespoons flour over the vegetables and stir for 1 minute, until it coats everything. This is what thickens the sauce into something creamy that clings to the tortellini.
Slowly pour in the 2 cups beef broth while stirring, then add the 1 cup heavy cream and 1 tablespoon Worcestershire sauce. Bring to a gentle simmer and cook for 3 to 4 minutes, until thickened enough to coat the back of a spoon.
Reduce the heat to low and stir in the 1½ cups provolone and ½ cup Parmesan, a handful at a time, until melted and smooth. Adding the cheese off the boil and in batches keeps the sauce silky instead of grainy.
Return the steak and any resting juices to the skillet, then add the cooked tortellini. Gently fold everything together until coated in the cheesy sauce and warmed through.
Sprinkle with the 2 tablespoons parsley and serve right away, while the cheese is at its meltiest.