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 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 doesn't need to be fully cooked yet.
Stir in the diced onion and cook for another 2 minutes until softened.
Add the penne, fire-roasted tomatoes with their juices, and chicken broth.
Stir well, cover, and bring everything to a boil.
Reduce heat to medium-low and simmer for about 10 minutes, stirring every couple of minutes until the pasta is tender and the sauce thickens.
Add chunks of cream cheese and stir until completely melted into the sauce.
Garnish with sliced green onions and serve your One Pot Creamy Cajun Chicken Pasta immediately.