I just did this recently myself, so while it’s still fresh in my mind, here’s a quick and dirty tutorial:
Let’s say you have a Linux laptop, and the headless Linux box where you want to run syncthing has a working hostname of “headless”, (within your LAN). The username on the headless box we’ll run Syncthing as is called “admsync”.
On the laptop, in a terminal:
ssh -L 9988:localhost:8384 admsync@headless
Then once ssh’ed in as admsync, run the syncthing command.
Now on your laptop, in a web browser, visit the URL:
…and you should see the Syncthing GUI from the headless box.
Note: on the headless box, in /etc/ssh/sshd_config, “AllowTcpForwarding” must not be “no”, for this tunneling to work.