Begin by bringing a large pot of salted water to a boil. Once boiling, add the dry rotini pasta and cook according to package instructions until al dente. Drain and set aside.
In a large skillet, melt the unsalted butter and olive oil over medium heat. Add the diced onion and green bell pepper, sautéing until the onion is translucent, about 3-4 minutes. Stir in the minced garlic and cook for an additional minute until fragrant.
Add the bite-sized pieces of chicken breast to the skillet. Sprinkle with Cajun seasoning and kosher salt. Cook until the chicken is browned and cooked through, about 6-8 minutes.
Pour in the chicken broth and add the can of fire-roasted diced tomatoes. Stir well to combine. Bring the mixture to a gentle simmer.
Reduce the heat to low and add the cream cheese cubes, stirring until melted and smooth. Then, slowly pour in the heavy cream, mixing until well combined and creamy.
Add the cooked rotini pasta to the sauce mixture, tossing to coat the pasta evenly. Let it cook for an additional 2-3 minutes to allow the flavors to meld.
Remove from heat and stir in the chopped green onions. Serve hot, garnished with extra green onions if desired.