1. Mix Worcestershire sauce, soy sauce, oyster sauce, ketchup, mirin, and sake together in a bowl. Set aside.
2. If using fresh yaki soba noodles, skip this step. For dried ramen noodles, boil them for 30 seconds less than the package directions. Drain thoroughly.
3. Heat 1 tablespoon of oil in a wok over medium-high heat. Add the sliced pork belly and cook for 5-9 minutes, until browned and crisp. Remove the pork belly from the wok and drain excess fat.
4. Add minced garlic and ginger to the wok and stir-fry for 30 seconds. Add the thinly sliced onion, cabbage, and carrot; cook for approximately 3 minutes, until tender. Remove the cooked vegetables from the wok and set aside with the pork.
5. Add the remaining 2 tablespoons of oil to the wok and heat on high for 1 minute. Add the noodles, spread them out, and press them down with a metal spatula. Cook for 2-3 minutes per side until crispy, then separate them into individual strands.
6. Return the cooked pork belly and vegetables to the wok with the noodles. Drizzle the prepared sauce around the wok and stir-fry for 2-3 minutes until the sauce is absorbed. Add the bean sprouts and cook for approximately 30 seconds more.
7. Top the finished yaki soba with thinly sliced nori and pickled ginger (if using) and serve immediately.
