In a medium bowl, mix together the soy sauce, sugar, sesame oil, Asian pear, scallions, garlic and ginger if using. Cut the pork into thin slices, trimming any fat and sinew as you go. Cut the slices into bite sized pieces then add to the marinade and mix. Leave to marinade a minimum of 30 minutes, but ideally a few hours or overnight.
When ready to cook, preheat grill pan to a medium-high heat. Take slices of the pork and cook in a single layer in batches on the grill pan, turning as you see the first side is starting to cook then just a minute or two more on the other side. They will cook quickly, so watch closely. As each batch cooks, set the pork aside and keep it warm.
Suggest serving with rice and your favorite Korean sides eg kimchi, or lightly seasoned veg such as those in my vegetarian bibimbap.
Times above don’t include marinating time. See other notes above for more tips.