Bring a large pot of salted water to a boil. Add the pasta and cook according to package directions until al dente. Reserve 1 cup of pasta water before draining.

While the pasta cooks, pat the steak cubes dry and toss them with 1 tablespoon of Cajun seasoning, salt, and pepper. Heat olive oil in a large skillet over medium-high heat. Add the steak and sear for 2-3 minutes per side until browned. Remove steak from the skillet and set aside.

In the same skillet, melt the butter over medium heat. Add the diced onion and bell pepper and cook until softened, about 5-7 minutes.

Stir in the minced garlic and the remaining 1 tablespoon of Cajun seasoning. Cook for 1 minute until fragrant. Pour in the heavy cream and bring to a simmer. Reduce heat and let it bubble gently for 2-3 minutes to thicken.

Stir in the grated Parmesan cheese until the sauce is smooth and creamy. Add the drained pasta to the skillet, tossing to coat. If the sauce is too thick, add a splash of the reserved pasta water.

Return the seared steak to the skillet and stir to combine. Garnish with fresh parsley and serve immediately.