Combine cauliflower and water in microwave-safe bowl. Microwave for 5 minutes or until cauliflower is tender. Drain and allow cauliflower to cool. Place cauliflower in a cheesecloth to squeeze out as much liquid as possible.
Mix 3/4 of the riced cauliflower with the parmesan cheese and egg. Reserve the 1/4 of riced cauliflower for later.
On a baking sheet lined with parchment paper, spread cauliflower mixture into 4 equally-sized circles that will fit the inside circumference of your serving bowls. Bake cauliflower crust at 400*F for about 4-8 minutes until center is dry and crust is golden brown.
Add the remaining ingredients to an Instant Pot, including the reserved riced cauliflower, to make the potpie filling. Secure lid, push meat/stew mode, and adjust time for 10 minutes. When Instant Pot beeps, naturally release pressure.
Ladle chicken potpie filling into bowls and top each with a cauliflower crust.