Use the bootadm generate-menu command to manually regenerate a grub.cfg file that contains the OS instances that are currently installed on a system.
Information from the /usr/lib/grub2/bios/etc/default/grub or the /usr/lib/grub2/uefi64/etc/default/grub file, combined with information from GRUB meta configuration file, rpool/boot/grub/menu.conf, is used to generate the final grub.cfg file.
See Using Your Assigned Administrative Rights in Securing Users and Processes in Oracle Solaris 11.2 .
# bootadm generate-menu
# bootadm generate-menu -f
# bootadm generate-menu -P pool-name
# bootadm list-menu