Chop the chicken into 1 inch pieces.
Heat a 12 inch skillet over medium heat and add the butter to melt. Stir to coat the pan.
Add the chicken to the skillet and sprinkle with half of the Cajun seasoning. Cook, stirring often, until the chicken is browned, about 5 minutes.
Add the onion and pepper to the pan and sprinkle with the remaining seasoning. Cook 5 minutes, stirring often.
Add the garlic and cook for 1 minute.
Add the penne, chicken broth, canned tomatoes, and half and half. Stir well to combine.
Bring to a boil, reduce to a simmer, and cover the pot.
Cook for 10-12 minutes or until pasta is tender.
Remove the lid and stir in the cream cheese to melt.
Stir in the spinach. Remove from heat, cover, and let sit for 5 minutes to wilt spinach.
Stir well before serving.