Finely shred the cabbage and set aside. If using thick-cut pork loin, butterfly each steak open and press it thin; score the edges to stop it curling. Pre-sliced pork can be used as is.
Lightly dust both sides of the pork with a thin coat of plain flour.
In a small bowl, mix the grated ginger, soy sauce, sugar, and cooking sake until the sugar dissolves.
Heat the sesame oil in a pan over medium heat. Fry the pork until lightly browned on both sides.
Add the sliced onion (if using) and cook until softened.
Once the pork is cooked through, stir the sauce and pour it in. Turn the pork in the sauce and let it reduce until glossy and coating everything, 1-2 minutes.
Plate with a mound of finely shredded raw cabbage, a dab of mayonnaise, and cherry tomatoes. Serve with rice and miso soup.