Make incisions around the edges of the pork loin slices and poke it with a knife.Mix the marinade ingredients in a container.
Spread the marinade on both sides of each slice of pork loin. Put the slices in the container with the remainder of the marinade and set aside in the fridge for at least 2 hours.
Heat oil in a pan over medium heat (if using a non-stick pan, oil isn’t necessary). Remove the excess miso marinade from the pork loin slices, and cook in the pan for about 5 minutes, covered, flipping halfway through.