df -ah | awk '{print $1 "\t" $6}' (and some manual editing)

Filesystem				Mounted on
zroot/ROOT/20190103-r342707		/
devfs					/dev
zdata/home				/home
zroot/media				/media
zroot/nfs				/nfs
zroot/tmp				/tmp
zroot/usr/compat			/usr/compat
zroot/usr/compat/linux			/usr/compat/linux
zroot/usr/docker			/usr/docker
zroot/usr/local				/usr/local
zroot/usr/local/certs			/usr/local/certs
zroot/usr/local/etc			/usr/local/etc
zroot/usr/local/info			/usr/local/info
zdata/usr/local/moodledata		/usr/local/moodledata
zdata/usr/local/pgsql			/usr/local/pgsql
zdata/usr/local/pgsql/data		/usr/local/pgsql/data
zdata/usr/local/pgsql/data/base		/usr/local/pgsql/data/base
zdata/usr/local/pgsql/data/pg_xlog	/usr/local/pgsql/data/pg_xlog
zroot/usr/local/tests			/usr/local/tests
zroot/usr/local/var			/usr/local/var
zdata/usr/local/www			/usr/local/www
zroot/usr/obj				/usr/obj
zroot/usr/ports				/usr/ports
zroot/usr/ports/distfiles		/usr/ports/distfiles
zroot/usr/ports/local			/usr/ports/local
zroot/usr/ports/packages		/usr/ports/packages
zroot/usr/ports/workdirs		/usr/ports/workdirs
zroot/usr/src				/usr/src
zroot/var/Named				/var/Named
zroot/var/account			/var/account
zroot/var/audit				/var/audit
zroot/var/backups			/var/backups
zroot/var/cache/ccache			/var/cache/ccache
zroot/var/cache/pkg			/var/cache/pkg
zroot/var/cache/synth			/var/cache/synth
zroot/var/crash				/var/crash
zdata/var/db/bacula			/var/db/bacula
zdata/var/db/bareos			/var/db/bareos
zdata/var/db/boinc			/var/db/boinc
zdata/var/db/darkstat			/var/db/darkstat
zroot/var/db/etcupdate			/var/db/etcupdate
zroot/var/db/fontconfig			/var/db/fontconfig
zroot/var/db/hyperv			/var/db/hyperv
zdata/var/db/mysql			/var/db/mysql
zdata/var/db/mysql_secure		/var/db/mysql_secure
zdata/var/db/mysql_tmpdir		/var/db/mysql_tmpdir
zroot/var/db/ntp			/var/db/ntp
zroot/var/db/pkg			/var/db/pkg
zroot/var/db/ports			/var/db/ports
zroot/var/db/portsnap			/var/db/portsnap
zdata/var/db/postgres			/var/db/postgres
zdata/var/db/postgres/data10		/var/db/postgres/data10
zdata/var/db/postgres/data10/base	/var/db/postgres/data10/base
zdata/var/db/postgres/data10/pg_wal	/var/db/postgres/data10/pg_wal
zdata/var/db/postgres/data11		/var/db/postgres/data11
zdata/var/db/postgres/data11/base	/var/db/postgres/data11/base
zdata/var/db/postgres/data11/pg_wal	/var/db/postgres/data11/pg_wal
zdata/var/db/postgres/data96		/var/db/postgres/data96
zdata/var/db/postgres/data96/base	/var/db/postgres/data96/base
zdata/var/db/postgres/data96/pg_xlog	/var/db/postgres/data96/pg_xlog
zdata/var/db/prometheus			/var/db/prometheus
zdata/var/db/prometheus/data		/var/db/prometheus/data
zdata/var/db/prometheus/data/wal	/var/db/prometheus/data/wal
zroot/var/db/tlpkg			/var/db/tlpkg
zroot/var/empty				/var/empty
zroot/var/lib				/var/lib
zroot/var/log				/var/log
zroot/var/mail				/var/mail
zroot/var/munin				/var/munin
zroot/var/run				/var/run
zroot/var/spool				/var/spool
zdata/var/spool/bareos			/var/spool/bareos
zroot/var/spool/clientmqueue		/var/spool/clientmqueue
zdata/var/spool/ftp			/var/spool/ftp
zroot/var/spool/mqueue			/var/spool/mqueue
zroot/var/synth				/var/synth
zroot/var/synth/builders		/var/synth/builders
zroot/var/synth/live_packages		/var/synth/live_packages
zroot/var/tmp				/var/tmp
zroot/var/unbound			/var/unbound
fdescfs					/dev/fd
procfs					/proc
devfs					/usr/compat/linux/dev
fdescfs					/usr/compat/linux/dev/fd
linprocfs				/usr/compat/linux/proc
linsysfs				/usr/compat/linux/sys