From https://help.ubuntu.com/community/Installation/MinimalCD
mini system in UEFI mode
While the minimal iso image is handy, it isn’t useful for installing on UEFI-based systems that you want to run in UEFI mode. The mini iso lacks the proper files for booting the computer in UEFI mode. Thus, the computer will boot in BIOS compatibility mode, and the installation will be in BIOS mode.
I’d use the ubuntu server iso.
