In a large pot or dutch oven, cook the pasta in salted water according to the package directions until it is al dente. Once cooked, drain the pasta and set it aside.
While the pasta is cooking, mix 2 teaspoons of cajun seasoning, garlic powder, onion powder, and 1/2 teaspoon of salt in a small bowl.
Sprinkle the seasoning mix over the chicken breast and mix until the chicken is coated.
Using the same pot you used to cook the pasta, drizzle a tablespoon of olive oil and heat it over medium-high heat. When the oil is hot, add the chicken and cook for 5-6 minutes on each side until the chicken is browned and cooked. Once cooked, remove the chicken from the pot and set it aside on a plate.
Drizzle the remaining olive oil in the same pot and add the onions and bell peppers. Cook over medium-high heat until the vegetables soften and the onions become translucent, which should take about 4 minutes.
Then, stir in the mushrooms and cook for 3-4 minutes or until the mushrooms soften.
Push the vegetables to the side of the pot and add the garlic. If needed, drizzle in a little more olive oil directly on the garlic and cook it for about 1 minute before stirring the vegetables together.
Stir in the chicken stock, scraping up any brown bits on the bottom of the pot.
In a small bowl, whisk together the flour and half and half until it forms a smooth slurry. Stir the slurry into the pot with the other ingredients.
Cook the vegetables and sauce over medium heat until it starts to bubble and the sauce begins to thicken. Note that the sauce will only thicken enough to cling to the pasta, which should take 3-5 minutes, and sometimes up to 6-7 minutes.
Stir in the grated cheese, the last 2 teaspoons of cajun seasoning, and 1/2 teaspoon salt. Taste the sauce and adjust the seasoning if necessary.
Add the chicken and pasta into the sauce and toss until evenly distributed. Continue cooking for 1-2 minutes or until the sauce coats the pasta and is hot. Serve with extra parmesan cheese.