Find a snug fitting container to hold the pork. Mix all the other ingredient in the container to make the marinade. Add the pork and turn it a few times to coat. Leave to marinate in the fridge for at least 6 hours, preferably overnight, giving it a turn every so often when you can.
Remove the pork from the fridge at least an hour before putting it on the BBQ. In the meantime, prepare any sides and get your BBQ lit so it has time to settle to a good medium-high heat.
Remove the pork, from the marinade and season it lightly with salt, not too much as the soy will have seasoned it well already. Place it on the BBQ and cook it on both sides for about 5 minutes until nicely coloured. Now shift the steak across to a more gentle, steady part of the BBQ and cook it for a further 25 minutes or so, turning often, until deeply coloured on all sides. Make sure you use your tongs to turn it so that each end and the thinner sides get time sat on the grill bars too, this ensures an even colour and cook. Brush and baste the steak with the remaining marinade every 5 minutes or so as you cook. The steak is done when it shows, between 65-70⁰C on a meat thermometer, or when it feels very firm when squeezed. You want it cooked all the way through with only the slightest blush to the meat. Leave to rest for at least 10 minutes before thinly slicing to serve.
This is perfect served alongside rice, stir-fried veg and fermented pickles, or tucked into bowls full of noodles and broth. It is great served hot or cold.