I do not like or approve of the currently highest rated answer as then you have to know your credentials into a script to do this and can’t do this from something like Packer or some other system/configuration automation. There is a better/proper way to do this which Aeyoun mentioned but didn’t go into details about which is to properly set the principal to run as the system user.
$action = New-ScheduledTaskAction -Execute foo.exe -Argument "bar baz"
$trigger = New-ScheduledTaskTrigger -Once -At (Get-Date) -RepetitionInterval (New-TimeSpan -Minutes 1) -RepetitionDuration ([Timespan]::MaxValue)
$principal = New-ScheduledTaskPrincipal -UserID "NT AUTHORITY\SYSTEM" -LogonType ServiceAccount -RunLevel Highest
$settings = New-ScheduledTaskSettingsSet -MultipleInstances Parallel
Register-ScheduledTask -TaskName "tasknamehere" -TaskPath "\my\path" -Action $action -Trigger $trigger -Settings $settings -Principal $principal