Preheat your oven to 375°F (190°C).

Cook the jumbo pasta shells according to the package instructions. Drain and set aside.

In a large skillet, heat olive oil over medium-high heat. Add the thinly sliced steak and cook until it's no longer pink. Remove the steak from the skillet and set it aside.

In the same skillet, add a bit more olive oil if needed. Sauté the sliced onion, green bell pepper, and mushrooms until they are tender. Season with salt, pepper, garlic powder, and onion powder.

Return the cooked steak to the skillet with the sautéed vegetables. Stir in the beef broth and let it simmer for a few minutes until most of the liquid has evaporated. Remove from heat.

In a mixing bowl, combine the cream cheese, 1 cup of mozzarella cheese, provolone cheese, Parmesan cheese, and chopped parsley. Mix until well combined.

Take each cooked jumbo shell and stuff it with a generous spoonful of the cheese mixture, then top with the Philly cheese steak mixture. Place the stuffed shells in a baking dish coated with cooking spray.

Once all the shells are stuffed and arranged in the baking dish, sprinkle with the remaining mozzarella cheese. Cover the dish with foil and bake in the preheated oven for 20-25 minutes or until the cheese is melted and bubbly.

Remove the foil and bake for an additional 5-10 minutes, allowing the tops to lightly brown.

Serve the Philly Cheese Steak Stuffed Shells hot, garnished with additional chopped parsley if desired.