Begin by cutting the chicken breasts into bite-sized pieces. In a large pot or deep skillet, heat the butter and olive oil over medium heat. Once hot, add the chicken pieces. Sear them until they're golden brown on all sides, about 5-7 minutes. It’s essential to get a nice sear; it adds depth to the flavor.

Next, add the finely chopped onion to the pot. Sauté for a few minutes until the onion becomes translucent. The aroma of the onion mingling with the chicken creates a welcoming scent that fills the kitchen.

Sprinkle the Cajun seasoning over the chicken and onion mixture. Stir well to ensure the chicken is evenly coated. The blend of spices will linger in the air, hinting at the flavor explosion to come.

Now, it’s time to add the fire-roasted diced tomatoes and chicken broth. Scrape any brown bits from the bottom of the pot; they pack loads of flavor. Bring the mixture to a boil.

Once boiling, add the uncooked penne pasta. Stir gently to ensure it’s evenly distributed. Bring it back to a simmer, then cover the pot. Cook for about 12 minutes or until the pasta is al dente. Stir occasionally, so nothing sticks.

After the pasta is cooked, remove the pot from heat. Stir in the softened cream cheese until it melts and creates a creamy sauce. It’s like watching magic unfold as the pasta transforms into a creamy delight.

Lastly, sprinkle the thinly sliced green onions and freshly chopped parsley on top. Give it one final stir for a nice touch of freshness. Serve in bowls and enjoy every mouthful.