Start by bringing a large pot of salted water to a boil. Add the penne pasta and cook according to package instructions until al dente—usually about 9 to 11 minutes. Once cooked, drain the pasta and set it aside, reserving about 1/2 cup of the pasta water to loosen the sauce later if needed.
Pat the salmon fillets dry with paper towels. Generously rub both sides with the Cajun seasoning, pressing it in to coat evenly. Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Carefully place the salmon fillets into the hot pan and sear for about 4 minutes per side, or until they develop a beautiful blackened crust and are cooked through. Remove the salmon from the pan and set aside.
In the same skillet, add the remaining tablespoon of olive oil. Toss in the diced onion, red bell pepper, and green bell pepper. Sauté for 4 to 5 minutes until softened and fragrant. Add the minced garlic, cooking for an additional 30 seconds to release its aroma.
Pour the heavy cream into the skillet with the sautéed vegetables, stirring to combine. Let the cream simmer gently for 2 to 3 minutes, allowing it to thicken slightly. Stir in the grated Parmesan cheese until melted and smooth. Season with salt and pepper to taste. If the sauce becomes too thick, add a splash of the reserved pasta water to reach your desired consistency.
Add the cooked penne pasta to the skillet, tossing gently to coat every piece in the creamy Cajun sauce. Break the salmon into large chunks and fold them carefully into the pasta mixture, trying not to break the fillets up too much.
Sprinkle freshly chopped parsley over the top for a vibrant finish. Serve immediately with a side of crusty bread or a light green salad for a complete meal.
