Set the Instant Pot to Saute and once it is hot add oil, butter, mushrooms, celery, and onion. Cook until the onion starts to become translucent.
Stir in broth, salt, pepper, and garlic powder.
Add the heavy cream and turn off of Saute
Add in the egg noodles, but do not stir.
Add in the tuna and spread it evenly over the noodles continuing not to stir.
Place lid on and set to Manual for 3 minutes on High Pressure. Keep in mind the pot itself will take a few minutes to come to pressure.
Once the cooking time has passed release the knob to the Venting position to release the steam. If the mixture begins to come out of the steam vent, close it and instead slowly release the pressure in small bursts.
Remove pot from the pressure cooker and set on a heat-safe surface to allow it to cool.
Add in the peas and give it a gentle stir.
While continuing to stir slowly add in the cheese, the casserole will begin to thicken and will continue to as it cools.
Notes
Want a crunchy topping?
Transfer cooked casserole to a baking dish.
Add a mixture of about ½ cup of panko, 1 tablespoon butter, and ½ cup parmesan cheese.
Then broil for just a few minutes until the topping is golden brown!!