Wrote this script with the help of Support. Thanks Ermins!

$days = 35
$system = Get-WmiObject win32_operatingsystem

if($system.ConvertToDateTime($system.LastBootUpTime) -lt (Get-Date).AddDays(-$days)){
    Restart-Computer -Force
}else{
    Write-Host "Machine was rebooted less than $days days ago"

}

Say I run this against 90 computers is there any way to get a notification of which computers rebooted?

All machines that reboot will timeout the script execution. So when you look at the task execution you will see it running for an hour if you don't stop it. The machines that reboot will show up as failed in the task execution results view.

-Paul