1..2 | % { [PSCustomObject] @{
    1 = Get-Random
    2 = Get-Random
    3 = ([PSCustomObject] @{ 4 = Get-Random; 5 = Get-Random }) | ConvertTo-Json
} } | Export-Csv -NoTypeInformation c:\temp\csvjson.csv

cat $$
$a = Import-Csv $$

$results = $a | % {
    $output = $_
    $3 = $_.3 | ConvertFrom-Json
    $3.PSObject.Properties | % {
        $output = $output | Add-Member $_.Name $_.Value -Pass
    }
    $output
}