Pat the chicken dry and cut into 1-inch cubes. Toss the chicken with 1/2 tablespoon of the Cajun seasoning until evenly coated.
Heat the olive oil in a large stockpot or deep skillet over medium-high heat. Add the seasoned chicken and cook, stirring occasionally, until the pieces are lightly browned on the outside, about 2–3 minutes per side.
Add the minced onion and diced red bell pepper to the pot and sauté for 2–3 minutes, until the onion begins to soften. Stir in the minced garlic and cook for 30 seconds until fragrant.
Pour in the chicken stock and undrained fire-roasted diced tomatoes. Add the remaining 1/2 tablespoon Cajun seasoning and stir, scraping up any browned bits from the bottom. Cover and bring to a boil.
Once boiling, remove the lid, add the rotini pasta, and reduce heat to medium-low. Cover and simmer, stirring every 2 minutes, until the pasta is tender and most of the liquid is absorbed, about 10 minutes.
Uncover, add the cubed cream cheese, and stir until it melts into a creamy sauce. Continue cooking uncovered, stirring frequently, until the pasta is fully cooked and sauce is smooth, about 4–5 minutes.
Garnish with sliced green onions and serve immediately.