In a large pot of boiling salted water, cook the rigatoni according to package instructions until al dente. Drain and set aside.
In a bowl, toss the steak strips with the Cajun seasoning until well coated.
In a large skillet, heat the olive oil over medium-high heat. Add the seasoned steak and sear for about 3-4 minutes until browned and cooked to your desired doneness. Remove the steak from the skillet and set aside.
In the same skillet, add the chopped onion and sliced bell peppers. Sauté for about 5 minutes until softened. Add the minced garlic and cook for an additional 1-2 minutes until fragrant.
Lower the heat to medium and pour in the heavy cream, stirring to combine. Gradually add in the grated Parmesan cheese, stirring until melted and the sauce is smooth.
Add the cooked rigatoni and seared steak back into the skillet. Toss everything together until the pasta and steak are well coated in the creamy sauce. Season with salt and pepper to taste.
Remove from heat and transfer to serving plates. Garnish with chopped parsley for a fresh touch.