function Get-MyDemoObject {
    $OBJ = @'
    "P1","P2","P3"
    "X","1","a"
    "Y","4","c"
    "Z","2","b"
    "Y","6","d"
'@
    $OBJ | ConvertFrom-Csv
}

Get-MyDemoObject | Where-Object { $_.P1 -eq "z"}
Get-MyDemoObject | Where-Object { $PSItem.P1 -eq "z"}