Gather all your ingredients: penne pasta, chicken, Cajun seasoning, onion, garlic, bell pepper, diced tomatoes, chicken broth, heavy cream, cheddar cheese, salt, pepper, and parsley.

Heat olive oil in a large pot or Dutch oven over medium heat. Add diced chicken breast and sprinkle with Cajun seasoning. Cook for 5-7 minutes until browned and cooked through. Remove chicken and set aside.

In the same pot, add chopped onion and bell pepper. Sauté for 3-4 minutes until onion is translucent. Add minced garlic and cook for an additional minute until fragrant.

Add penne pasta, diced tomatoes (with juices), and chicken broth to the pot. Bring to a boil, then reduce heat to a simmer. Cover and cook for 12-15 minutes, stirring occasionally, until pasta is al dente.

Stir in heavy cream and additional Cajun seasoning. Mix well until the sauce is smooth. Season with salt and pepper to taste.

Return the cooked chicken to the pot and stir to combine. Add shredded cheddar cheese and mix until melted into the sauce. Garnish with freshly chopped parsley before serving.