Bring a big pot of salted water to a boil and cook the noodles according to the package instructions. Drain and set aside.
To prepare the jackfruit, cut off the hard cores, remove any seeds and seed pods and discard. Shred the rest, leaving some chunkier pieces. Set aside.
Heat a wide shallow pan or Dutch oven over medium heat. Add the sunflower oil. When it’s shimmering, add the onions and cook until translucent, about 5 minutes. Add the garlic and ginger. Cook until the garlic and ginger are fragrant, about 1 minute.
Add the jackfruit and water and use tongs to mix around. Cook with the cover askew, until most of the water is absorbed, about 10 to 12 minutes.
Add the mushrooms. Stir them into the jackfruit and onion mixture and cook, until the mushrooms start to turn golden brown, about 7 minutes. Season with salt and pepper.
Add the carrots and bok choy. Cook until the bok choy is wilted and bright green, about 3 to 5 minutes. Add the noodles and toss everything together.
In the meantime, prepare the sauce. Add the water, tamari, umeboshi paste, miso and mirin to a small mixing bowl. Break up the miso with a small silicone spatula and whisk the sauce together until completely smooth.
Pour the sauce over the top and use tongs to mix it until everything is fully coated.
Serve topped with scallions.