XPS 8910, cannot add UEFI boot option?

Figured it out. In order to add the UEFI HDD boot option back (when missing) you have to do the following:

1. Ensure your computer supports UEFI mode, which most recent computers support
2. Ensure your HDD is currently using a MBR partition table | instructions here
3. Ensure your computer has Windows 10 version 1703 or later
4. Use a clever Microsoft tool called MBR2GPT to convert your MBR drive to a GPT drive without any data loss
   • Boot into a Windows installation disk/drive and then press Shift + F10 keys together on the keyboard to open a command prompt window
   • Launch diskpart by entering the command: diskpart 
     • NOTE If this didn't work, you may have to type: cd .. to move back one directory and then try again
   • Display all disks by typing the command: list disk
   • Find the disk number the corresponds with the disk you would like to convert. Take note of this for next steps.
   • Type the command exit to exit the diskpart program
   • This is the important one. Type: mbr2gpt /convert /disk:0  With 0 being the disk number you wanted to convert. Wait for this to complete...
   • Now you can exit out of this command prompt and shut down the computer.
5. You now need to boot into the BIOS and enable UEFI mode.
6. Check the boot list for the deleted boot option. If not present, you need to add it back manually
   • Select "Add boot option"
   • Set name to "HDD"
   • Change File System List to the correct one
     • Tip: this should contain something along the lines of SATA and GPT
   • Change the File Name to \EFI\Boot\bootx64.efi
7. Save and apply these changes. You should now be able to boot using a UEFI drive option.
8. Next time, when tinkering with alternate operating systems always install to a GPT partition table ;)

 Hope this helps somebody!

- Luke