Mount everything correctly:

zpool export -a
zpool import -N -R /mnt rpool
zpool import -N -R /mnt bpool
zfs load-key -a
# Add “UUID” at the end, if appropriate; use zfs list to see your values:
zfs mount rpool/ROOT/ubuntu
zfs mount bpool/BOOT/ubuntu
zfs mount -a

If needed, you can chroot into your installed environment:

for i in proc sys dev run tmp; do mount -o bind /$i /mnt/$i; done
chroot /mnt /bin/bash --login
mount -a

Do whatever you need to do to fix your system.

When done, cleanup:

exit
mount | grep -v zfs | tac | awk '/\/mnt/ {print $3}' | \
    xargs -i{} umount -lf {}
zpool export -a
reboot