Put the steamer basket in the pressure cooker pot. Add the water, potatoes, and the eggs. Lock lid in place, select High Pressure, 4 minutes cook time and press start.
When timer beeps, turn off pressure cooker and do a quick pressure release. When the pressure is released, carefully remove the lid. Remove the steamer basket from the pressure cooking pot. Put eggs into ice cold water to cool.
In a large bowl, combine the onion, mayo, parsley, pickle juice, and mustard. Add cooled potatoes and gently mix the mayonnaise mixture into the potatoes. Peel and dice three of the cooled eggs and stir into potato salad. Add salt and pepper to taste. If needed, add more mayonnaise to achieve desired consistency.
Chill at least one hour before serving. Top with slices of remaining hard boiled egg.