Place the penne pasta in the instant pot and fill with enough water to cover the noodles. Close the lid and seal your lid by pushing the valve away from you. Set to high pressure for 8 minutes.
Once your cook time is complete, do a quick release by bringing the valve toward you to open the pressure.
Drain your noodles and place in a separate bowl. Set aside.
Chicken
You can choose to cook your chicken:
On the side in the skillet while your pasta is cooking. Season your chicken with the Cajun seasoning.
In the instant pot after you are done cooking your pasta. Set to sauté mode. Add 4 tablespoons of oil (enough to cover the center of your pot). Season with your Cajun seasoning and slice your chicken into strips and sauté (or cook whole, then slice later). Cook until the inside of your chicken reaches 165°.
You can also pressure cook your chicken whole by placing the trivet inside, adding 1 cup of water, and placing your seasoned chicken (sprinkle with Cajun seasoning) on the trivet. Close lid as well as sealing valve. Set to High Pressure for 10 minutes. Quick release when done. Remove water.
Sauce
Continue to keep your instant pot on sauté mode. Add in your butter, half-and-half, lemon zest, pepper, salt, and garlic powder to your pot. Continue to stir until it starts to bubble.
Add your pasta to your pot and sauce. Mix well.
Transfer your pasta to your serving dish. Top with a few strips of chicken, diced tomatoes, and as much Parmesan cheese as you want! Enjoy!