Place a large high-sided skillet or medium-sized soup pot with a tight-fitting lid over medium-high heat and melt butter. Add diced chicken then sprinkle with Cajun seasoning.
Cook 10–12 minutes, stirring frequently until chicken is nicely browned and cooked through. Transfer chicken to a plate then cover with foil to keep warm and set aside.
Return skillet to heat then add garlic. If necessary, add a bit more butter and cook garlic for about 30 seconds, just to soften, then pour in chicken broth. Add pasta, making sure it is completely submerged in liquid
Stir pasta frequently to avoid sticking until liquid comes to a boil. Reduce heat to low then cover and cook about 10–12 minutes until pasta is tender but still firm, stirring occasionally. The pasta should absorb nearly all of the broth.
Add half-and-half then allow it to heat up before adding cream cheese. Stir until cream cheese is completely melted then stir in Parmesan cheese. Remove from heat then add tomatoes, green onions and reserved chicken and stir to combine.
Replace the lid and allow dish to rest covered for 5 minutes to allow sauce to thicken and chicken to re-heat. Prior to serving, give pasta a good stir. Season to taste with salt and fresh black pepper. If the sauce gets a bit too thick, thin it with a touch of milk.
One Last Thing
Cajun seasoning blends are available in the spice aisle and contain varying amounts of salt; this why we seasoned the dish with salt and pepper last.