In a small bowl, whisk together Worcestershire sauce, oyster sauce, ketchup, soy sauce, and sugar until fully combined. Taste and adjust sweetness depending on the flavor of your Worcestershire sauce or ketchup—some may be more tart or sweet than others. Set the sauce aside for later use.

Place the pork belly slices in the freezer for about 10 minutes to firm them up slightly, making them easier to slice. Cut them into 1-inch (2.5 cm) pieces. Thinly slice the onion, julienne the carrot into 2-inch (5 cm) matchsticks, and chop the cabbage into small, bite-sized portions. Slice the shiitake mushrooms into ¼-inch (6-mm) pieces, and cut the green onions into 2-inch (5-cm) sections, halving any thick white portions lengthwise for even cooking.

Heat a large griddle, wok, or heavy frying pan over medium heat. Once hot, add 2 tablespoons of neutral oil. Place the pre-steamed yakisoba noodles directly onto the griddle without loosening them first. Let one side heat up before gently flipping the noodles. Use chopsticks or tongs to slowly loosen the strands—avoid forcing them apart, as this can cause breakage. Once the noodles have softened and separated, transfer them to a plate and set aside.

Return the griddle or wok to medium heat. Add the sliced pork belly, spreading it into a single layer. Season lightly with freshly ground black pepper and stir-fry until the meat is no longer pink. If using another protein, add 1 tablespoon of oil before cooking.

Add the onion slices, stirring for 1–2 minutes until they begin to soften and separate. Next, add the carrots and continue stir-frying for another minute. Toss in the cabbage and shiitake mushrooms, cooking until they’re almost tender but still slightly crisp. Finish by adding the green onions, stir-frying briefly for about 1 minute.

Place the cooked yakisoba noodles on top of the vegetables and meat. Pour in about ⅓ cup of the prepared sauce, drizzling it evenly over the noodles. Using tongs, toss the mixture until the sauce coats every strand and the ingredients are evenly distributed. Adjust the amount of sauce to your liking. Keep stirring until the noodles are hot and glossy, being careful not to let them stick to the pan.

Transfer the Yakisoba to individual plates or a large serving platter. Garnish generously with aonori flakes and pickled red ginger for authentic Japanese flair. Serve immediately while hot for the best flavor and texture.