Hardmod: adding relay or MOSFET for power cycling 12V DC device

My network setup includes Turris Omnia and ISP-provided ONU terminal connected to the WAN port of the Turris Omnia.

ONU terminal is powered by IEEE 802.3af PoE and so, there’s a PoE injector installed between these network devices (specifically, the ONV PSE3101DCG).

Key feature of this PoE injector is 12V DC power input jack, so it has a shared power source with Omnia. ONU terminal consumes about 6W, so current consumption by the PoE injector is well below 1A.

ISP-provided ONU terminal occasionally hangs, so it needs a power cycling to continue operating. Currently this power cycling is performed manually, and I would like to automate this process (preferably with a script running on my Turris Omnia).

I have some soldering experience and I can, for example, solder a small PCB with relay or a MOSFET with few resistors inside the case of my router.

From a hardware standpoint, what is the best way to add such software-controlled 12V 1A DC switch to the Omnia? I’ve overheard of Turrisduino connector on the Omnia PCB, are there some suitable GPIO pins that can drive a MOSFET? Maybe the router already has some 12V power sources gated by software-controlled MOSFETs (e.g. for SATA storage devices etc)? Or should I leave the router alone and just buy an external USB relay?

My hardware revision is RTROM01-2G if that matters.

I wouldn’t recommend coupling the power cycling with the Omnia. Coupling like that may cause unknown reliability issues in your setup. You could consider using a simple timer instead.

Perhaps something like this: Countdown timer module