Combine all Cajun seasoning ingredients in a small bowl. Cube the chicken and toss it with the seasoning to fully coat.
Heat the oil and butter in a deep skillet over medium-high heat. Add the seasoned chicken and cook for a few minutes on each side until browned (it does not need to be cooked through).
Add the diced yellow onion and sauté for about 2 minutes until it begins to soften, scraping up any browned bits from the skillet.
Add the pasta, fire roasted diced tomatoes (with juices), and chicken broth. Stir well to combine.
Bring the mixture to a boil with a lid on. Once boiling, reduce the heat to medium-low and simmer for about 10 minutes, stirring every 2 minutes, until the pasta is tender and the liquid has thickened into a sauce.
Remove from heat, add the cream cheese in chunks, and stir until it has melted completely into a smooth, creamy sauce.
Top with sliced green onions and serve hot.