In a bowl whisk eggs, then add milk and seasonings. Stir in sliced mushrooms.
Spray the inside of your 6" round pan with non stick spray. Spread cheese on the bottom and spread out evenly. Pour egg mixture on the top.
Put trivet on the bottom of the pressure cooker, pour water inside. Place filled pan on top of trivet.
Pressure cook on high for 25 minutes with a 10 minute natural release. Release rest of steam and quickly remove lid flipping upside down so condensation doesn't fall on to the top of the quiche.
Allow to cool for 10-15 minutes in pan. Slide knife around outside to release. Release outside of springform pan if used and transfer to a plate to serve.