External powershell scripts only run once when action called - powershell

Question

I am trying to call an outside ps script to run every time files are created. The monitoring and logging of files work well, but the Invoke-Expression of running the external script only runs one time even if more files are created. How do I run the external script with every time a new file is created.
### SET FOLDER TO WATCH + FILES TO WATCH + SUBFOLDERS YES/NO
$watcher = New-Object System.IO.FileSystemWatcher
$watcher.Path = "c:\mypath"
$watcher.Filter = "*.txt*"
$watcher.IncludeSubdirectories = $true
$watcher.EnableRaisingEvents = $true
### DEFINE ACTIONS AFTER AN EVENT IS DETECTED
$action = { $path = $Event.SourceEventArgs.FullPath
$changeType = $Event.SourceEventArgs.ChangeType
$logline = "$(Get-Date), $changeType, $path"
Add-content "C:\mypath\log.txt" -value $logline
Invoke-Expression (start powershell ("C:\MyOtherScript.ps1")) ###### This only runs one time even if file is changes and logged
}
### DECIDE WHICH EVENTS SHOULD BE WATCHED
Register-ObjectEvent $watcher "Created" -Action $action
while ($true) {sleep 5}
EDIT: This got it working incase anyone find themselves here looking to solve the porblem
### SET FOLDER TO WATCH + FILES TO WATCH + SUBFOLDERS YES/NO
$watcher = New-Object System.IO.FileSystemWatcher
$watcher.Path = "c:\mypath"
$watcher.Filter = "*.txt*"
$watcher.IncludeSubdirectories = $true
$watcher.EnableRaisingEvents = $true
### DEFINE ACTIONS AFTER AN EVENT IS DETECTED
$action = { $path = $Event.SourceEventArgs.FullPath
$changeType = $Event.SourceEventArgs.ChangeType
$logline = "$(Get-Date), $changeType, $path"
Add-content "C:\mypath\log.txt" -value $logline
Start-Process powershell -argument "C:\MyOtherScript.ps1"
}
### DECIDE WHICH EVENTS SHOULD BE WATCHED
Register-ObjectEvent $watcher "Created" -Action $action
#while ($true) {sleep 5}

Answer 1

Invoke-Expression is not recommend over using & due to security concerns. In your example, however, I'd suggest Start-Process:
Start-Process -FilePath 'powershell' -ArgumentList #('-File','"C:\MyOtherScript.ps1"')