In a small bowl, combine the smoked paprika, oregano, thyme, garlic powder, onion powder, cayenne pepper, black pepper, and salt.
Cut the chicken into bite-sized cubes and toss with the Cajun seasoning until evenly coated.
Heat the olive oil and butter in a large deep skillet over medium-high heat.
Add the seasoned chicken and cook for 2–3 minutes per side until lightly browned. The chicken does not need to be fully cooked at this stage.
Add the diced onion and sauté for about 2 minutes until softened, scraping up any flavorful browned bits from the bottom of the skillet.
Stir in the uncooked penne, fire-roasted diced tomatoes with their juices, and chicken broth.
Bring the mixture to a boil, then reduce the heat to medium-low. Cover and simmer for about 10 minutes, stirring every few minutes until the pasta is tender and most of the liquid has thickened into a creamy sauce.
Add the cream cheese in small pieces and stir until completely melted and incorporated into the sauce.
Sprinkle with sliced green onions and serve immediately. This One Pot Creamy Cajun Chicken Pasta is best enjoyed hot with freshly grated Parmesan if desired.