Use a spoon to scrape off the ginger skin. Grate it over a bowl to catch all the juice. About 1 tablespoon would be enough. In a small container, combine the grated ginger with the soy sauce, mirin, sake, sugar, and water. Mix well.

Slice the onion into ¼-inch (0.5 cm) thick slices. Thinly slice the cabbage. Soak it in cold water for 1 to 2 minutes to remove any bitterness and keep it crisp and fresh. Drain and set aside. (It will complement the ginger pork and the sauce, adding a nice crunch.)

Thinly slice the pork loin. Make a few slashes along the edges of each pork slice to prevent curling while cooking. Season both sides with black pepper. If the slices are thick, add a little salt, but not too much.

Lightly coat the pork with potato starch. This creates a thin layer that locks in the meat's juices, preventing it from drying out while cooking. It also helps the pork absorb more of the delicious ginger sauce, making it even juicier. (Cornstarch or all-purpose flour can be used as alternatives.)

In a large pan, heat 1 tablespoon of oil over medium-high heat. Add the sliced onions with a pinch of salt. Saute for 3 to 4 minutes or until softened and browned. Remove and set aside.

In the same pan, add 1 tablespoon of oil over medium-high heat. Once hot, working in two batches, add the pork slices in a single layer. Cook for 1 to 2 minutes per side or until no longer pink. Do not overcook, as pork can easily get dry and tough.

Once all batches are done, reduce the heat to medium. Return all the pork and onions to the pan. Give the sauce a quick stir and pour it in. Let it bubble and simmer for 2 to 3 minutes, flipping the pork pieces occasionally to coat them well.

Meanwhile, optionally, grill some shishito peppers to use as a garnish.

When the sauce has thickened and the pork is nicely coated, plate the shogayaki (Japanese ginger pork). Serve with a generous portion of shredded cabbage and steamed rice. Garnish with grilled shishito peppers and cherry tomatoes. Drizzle some sauce from the pan. Enjoy!