To the Instant Pot, add the olive oil, chicken, penne pasta, chicken broth, red onion, garlic, fajita seasoning, kosher salt, and ground black pepper. Make sure the pasta is submerged in liquid.
Add the diced tomatoes on top (do not mix).
Close the Instant Pot and set the valve to the "SEAL" position. Pressure cook on “HIGH” for four minutes. When done, quickly release the pressure.
Open the Instant Pot, add the heavy cream, and quickly mix well.
Add the sliced bell peppers and close the Instant Pot for a few minutes to allow the peppers to soften.
Mix everything together well, then serve with garnishes and toppings of choice.