In a medium bowl, soak the noodles in hot water until they are easy to separate with your fingers, then drain and set aside.
In a medium bowl, whisk together the dark soy sauce, mirin, vegan fish sauce, light brown sugar and mushroom seasoning (if using) until well combined. Set the sauce aside.
Heat the vegetable oil in a large pan or wok over high heat. Add the ginger and spring onions, sautéing for about a minute until fragrant.
Add the shredded cabbage, julienned carrot, sliced shiitake mushrooms and edamame beans to the pan. Stir-fry the vegetables for about 3-4 minutes until they are just tender but still have some crunch.
Add the soaked and drained udon noodles to the pan with the vegetables. Toss to combine and heat through, ensuring the noodles are fully separated.
Pour the prepared sauce over the noodles and vegetables in the pan. Stir everything together so that the sauce coats the noodles and veggies evenly. Allow the mixture to simmer for 3-5 minutes, or until the sauce has reduced slightly and everything is well coated.
Serve the yaki udon hot, garnished with a sprinkle of toasted sesame seeds and additional chopped spring onions.
