Solved it by using \" as the inner quotes. Had to swap ' with \\\`" in PowerShell script
$command = "PowerShell \`"& \\\`"C:\ProgramFiles (x86)\MyDir\MyScript.ps1\\\`" $myStringParam $myBooleanParam\'""
So Task Scheduler shows
PowerShell "& \"C:\Program Files (x86)\MyDir\MyScript.ps1\" Cat 0"