In your large pot or Dutch oven, melt the salted butter over medium-high heat. Once melted, add the cubed chicken, along with 2 teaspoons of Cajun seasoning. Cook for about 5-7 minutes, stirring occasionally, until the chicken is browned and cooked through.
Add the sliced onion, chopped poblano peppers, and garlic to the pot. Sauté for an additional 3-4 minutes until the vegetables are softened and fragrant.
Stir in the short cut pasta, followed by 2 cups of milk, and the remaining Cajun seasoning. Bring the mixture to a gentle boil, then reduce the heat to low. Cover the pot and let it simmer for about 10-12 minutes, or until the pasta is al dente, stirring occasionally to prevent sticking.
Once the pasta is cooked, add the cream cheese, ranch dressing, and grated parmesan cheese. Stir everything together until the cheese is melted and the sauce is creamy and well combined.
Remove the pot from heat and stir in the fresh parsley. If you like a little heat, sprinkle with chili flakes to taste. Serve warm, garnished with extra parsley or parmesan cheese if desired.