Bring a large pot of salted water to a boil and add the cheese tortellini. Cook according to package instructions, about 3-5 minutes, until they float and are al dente. Drain and set aside.

In a large skillet, heat 1 tablespoon of olive oil over medium-high heat. Add the beef sirloin, seasoned with salt and pepper, and sear for about 5 minutes until browned. Remove and rest.

In the same skillet, add more olive oil if needed, and lower the heat to medium. Add diced green bell pepper and onion, cooking for 5-7 minutes until tender. Add minced garlic and sauté for another minute.

Melt 3 tablespoons of butter in a separate saucepan over medium heat. Stir in 3 tablespoons of all-purpose flour, cooking for about 1 minute. Gradually whisk in 2 cups of whole milk, stirring for 3-4 minutes until thickened.

Stir in 1 cup of shredded provolone cheese and 1/2 cup of grated Parmesan cheese into the thickened sauce until melted and smooth. Season with salt and pepper to taste.

Fold the cooked tortellini, seared beef, and sautéed vegetables into the creamy cheese sauce, stirring gently for about 2 minutes over low heat.

Spoon the Cheesesteak Tortellini onto plates while hot, garnishing with fresh parsley or additional Parmesan cheese. Serve immediately.