Start a Service After Mounting a Filesystem

With the filesystem mounted, use systemctl list-units --type=mount to locate the unit's name.

Then use a unit file following this template, in /etc/systemd/system/*.service

[Unit]
Description=My Service
After=${MOUNT_POINT_UNIT_NAME}

[Service]
Type=oneshot
RemainAfterExit=true
User=attie
Group=attie
ExecStart=${MY_SERVICE}

[Install]
WantedBy=multi-user.target

Subsequently, run the following to enable to service:

systemctl enable ${SERVICE_NAME}

Reference for the unit files here.