Prepare the chicken by cutting it into bite-sized pieces and coating it with Cajun seasoning.
Cook the penne pasta in salted boiling water until al dente, about 8-10 minutes, then drain.
In a large skillet, heat olive oil and cook the seasoned chicken for 5-7 minutes until browned and cooked through.
Sauté diced onion for 3-4 minutes, then add minced garlic and cook for an additional minute.
Pour in heavy cream and chicken broth, stir, and simmer for 3-4 minutes until slightly thickened.
Add diced tomatoes and shredded cheddar cheese, stir until cheese melts, then return chicken and add drained pasta, tossing to combine.
Season with salt and pepper, garnish with parsley, and serve immediately.