In a small bowl, combine all the spices for the Cajun seasoning. This blend serves as the flavor base. Once mixed, set aside.

Start a pot of salted water boiling. Add the penne pasta and cook it according to package instructions. Drain once al dente, reserving some of the pasta water.

In a large skillet over medium heat, warm the olive oil. Add the chopped onions and cook until they're translucent. This process makes room for the next depth of flavor.

To the skillet, increase the heat slightly and add the diced chicken. Make sure to season with the Cajun spice blend. Brown the chicken on all sides. You want those spices to infuse into the meat.

Lower the heat, add in the chicken broth and fire-roasted tomatoes along with their juices. Allow these to simmer. Now’s the time to mix in that cream cheese. Stir until it melts and blends beautifully with the other ingredients.

Fold the pasta into your skillet mixture, ensuring it's coated in that creamy sauce. If it seems a bit thick, use that reserved pasta water to loosen it up.

Finally, stir in fresh lemon zest and green onions. These bright notes will elevate the dish from rich to refreshing.

Dish out the pasta to hungry plates, sprinkling extra green onions on top for garnish.