Data Recovery after format and OS re-install

After about twenty years, I felt ZAR can no longer be updated to match the modern requirements, and I decided to retire it.

ZAR is replaced by Klennet Recovery, my new general-purpose DIY data recovery software.

If you are looking specifically for recovery of image files (like JPEG, CR2, and NEF), take a look at Klennet Carver, a separate video and photo recovery software.

My computer tech formatted the hard drive and re installed OS assuming that the data was already backed up. Is there any way the data can be recovered? I am more interested in the outlook data that was saved on my system. I can't afford to lose the emails.

After reinstall, on NTFS, the data may still be recovered until either MFT entry for the file, or the file data is overwritten. An installation itself writes significant amounts of data onto the disk (including temporary files, which are quite large), inducing massive damage.
So recoveries after reinstall are difficult but still can sometimes be successful.
You should try our demo as described in the unformat tutorial

Can I recover data from the disk which was fully formatted and operating system loaded?

Actually, there are two types of disk format - quick format and complete (also known as "full") format. After quick format the data is still recoverable while after complete format no, because each sector on a disk was overwritten. However, most factory repair disks use the quick format, so I think that in your case it makes sense to try to recover data because most likely it was a quick format rather than full.