Most desktop motherboard with UEFI has a legacy/compatibility mode which allow you to boot Linux using the Lilo/Grub/Syslinux and you can install Slackware just like usual. I have an Asrock board and it's called boot in AHCI, yours maybe different though.
But if you want to run Slackware on pure UEFI mode (not legacy/compatibility mode), you're going to need some things to do. The website http://www.rodsbooks.com
provides many valuable information regarding running Linux on UEFI enviroment, including the new partition layout (GPT)