I have installed Ubuntu Server 18.04 onto software RAID1 using the manual disk setup as described here: https://help.ubuntu.com/lts/serverguide/advanced-installation.html.en
However, I would like to boot via UEFI, and this method does not seem to create an EFI partition. Indeed, it sets up an MS-DOS partition table instead of the GPT partition table that I would need for UEFI boot.
So I tried going the manual route following the procedure here: https://gist.github.com/umpirsky/6ee1f870e759815333c8
However this is designed to work with the ubiquity installer, and anyway I can't even get past the first step because I can't use apt-get in the installer. I tried selecting "execute a shell" at the beginning of installation, but it seems there is not apt present at that point (command not found). I also tried booting from a Gparted rescue USB (Debian based), but from there I could not install grub-efi-amd64 (no installation candidate).
Is there a good, up-to-date tutorial about my specific situation? Or how might I modify the procedures linked to above to my purposes?