Boil a large pot of salted water over high heat. Add rigatoni and cook for 10-12 minutes until al dente. Reserve 1 cup of pasta water and drain the rigatoni.

Season the sirloin steak with Cajun seasoning. Heat olive oil in a skillet over medium-high heat. Add steak and sear for 3-4 minutes on each side until browned. Remove and let rest.

In the same skillet, reduce heat to medium. Add chopped onion and diced bell pepper. Sauté for 3-4 minutes until softened. Add minced garlic and sauté for 1 minute until fragrant.

Stir in canned diced tomatoes and simmer for 5 minutes until the tomatoes burst.

Lower heat and add heavy cream, stirring until smooth. Gradually add Parmesan cheese, stirring until melted. Adjust consistency with reserved pasta water if needed.

Return the seared steak to the skillet and coat it with the sauce for 2-3 minutes to heat through.

Add drained rigatoni to the skillet, stirring to coat with sauce. Season with salt and pepper to taste.

Serve hot, garnished with chopped parsley and extra Parmesan cheese if desired.