How do I fix this?
It shows for a few sec and then starts the OS. It's annoying.
First and for most, please make sure that you are using boot UEFI in the BIOS. Because from what I understand, this is the type of message you can get, if you are trying to boot a modern Linux OS in LEGACY mode.
Already in UEFI.
It shows every time I turn on/restart my computer. It makes me waste a few seconds every time.
Are Secure Boot and Fast Boot turned off? Is this a Dual-Boot System?
So, it does boot into Zorin OS? Have you done anything to the drive in terms of resizing partitions, etc?
When you get the chance, please launch a terminal and run cat /etc/fstab. You should get something like this:
# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point> <type> <options> <dump> <pass>
# / was on /dev/vda3 during installation
UUID=28d33b6b-0e35-422b-b71a-1e4803e24aba / ext4 errors=remount-ro 0 1
# /boot/efi was on /dev/vda2 during installation
UUID=20C5-8B53 /boot/efi vfat umask=0077 0 1
/swapfile