Coat the inside of a silicone mold with nonstick spray
Firmly press the asiago cheese into the bottom and slightly up the sides of the silicone mold. Top with diced mushrooms, chives and spinach.
Combine the eggs, cream, garlic salt and salt in a medium bowl and whisk thoroughly. Pour into molds. Molds should not be more than 3/4 full.
Pour 1 cup of water in the Instant Pot and insert the trivet. Carefully lower the mold on to the trivet. Secure the lid, making sure the vent is closed.
Using the display panel select the MANUAL or PRESSURE COOK function*. Use the +/- buttons and program the Instant Pot for 5 minutes.
When the time is up, let the pressure naturally release for 5 minutes, then quick-release the remaining pressure.
Carefully remove the mold and turn out onto a plate while still warm. Immediately flip each mini quiche so that the mushrooms are on top and press down lightly with fingers to flatten the bottom of each quiche.
Garnish with additional asiago cheese if desired. Serve warm.
*If your Instant Pot does not have a MANUAL function, use the Pressure Cook function.