Bring a large pot of salted water to a boil and cook the penne according to package directions until al dente.
While the pasta cooks, season the chicken pieces evenly with half of the Cajun seasoning.
Heat olive oil and 1 tablespoon of butter in a large skillet over medium-high heat.
Add the chicken to the skillet and cook until golden brown and cooked through, then remove and set aside.
In the same skillet, add the remaining butter, diced onion, and bell pepper, sautéing until softened.
Stir in the garlic and the remaining Cajun seasoning, cooking until fragrant.
Reduce heat to medium-low, add heavy cream and cream cheese, whisking until smooth and melted.
Stir in the grated Parmesan cheese until the sauce thickens slightly.
Add the cooked chicken and pasta to the sauce, tossing until thoroughly coated.
Garnish with parsley and serve immediately.