Press on SAUTE on the Instant Pot, add oil and melt the butter. Then add the mushrooms and saute them for a couple of minutes.
Add the chicken, season with salt and Italian seasoning and saute for a couple of more minutes. Then add the garlic, and cook for a minute. Switch off the SAUTE setting.
Add pasta, and cover with stock. The pasta MUST be covered, so add more stock or water to top it up and gently press the pasta down with a spatula or wooden spoon to make sure that it's covered in liquid.
Secure the lid and set the vent to SEALING. Select the PRESSURE COOK/MANUAL setting and set the cooking time for 4 minutes at high pressure. The Instant Pot will take around 6-7 minutes to come to pressure and start cooking. When the cooking program ends, quickly release the steam.
Remove the lid, give the pasta and chicken a quick stir and stir in the cream and parmesan. If you're having trouble to melt the cheese, it means that the pasta is not hot enough to melt it. So just switch on the SAUTE setting, and stir. If the sauce is too liquidy, thicken with a cornstarch slurry. Just add 1 tablespoon of cornstarch mixed with 1 tablespoon of water, add them to the sauce and stir until the sauce thickens (you don't want it too thick, as it thickens more once it cools down).
Add the baby spinach leaves and stir until they wilt. Garnish with extra grated parmesan cheese and serve warm!