Cook the whole wheat penne according to package directions; drain, rinse under cold water, and set aside.
Heat the olive oil in a large deep skillet or soup pot over medium-high heat.
Add the chopped onion, red and green bell peppers, and minced garlic; sauté until the vegetables are softened and the garlic is fragrant, taking care not to burn it, about 4–5 minutes.
Add the andouille sausage cubes and sauté until heated through, about 5 minutes, stirring occasionally.
Stir in the Cajun seasoning and the shredded cooked chicken; cook until the chicken is heated through, about 2–3 minutes.
Add the cooked penne to the skillet and stir to combine with the meat and vegetables.
Slowly pour in the skim milk and bring the mixture to a gentle simmer; cook for about 5 minutes to meld flavors.
Optional: In a small bowl, whisk the cornstarch (or arrowroot/tapioca) with the chicken broth until smooth, then pour into the simmering pasta and stir until the sauce thickens.
Stir in the shredded low-fat Parmesan until melted and combined, then remove from heat and serve.