Begin by preparing the shrimp. In a bowl, combine the shrimp with dark soy sauce, vegetable oil, and cornstarch. Mix thoroughly to coat each piece evenly, then set aside to marinate while you prep the rest.
In a separate bowl, whisk together all the ingredients for the stir fry sauce until smooth. This includes the dark soy sauce, oyster sauce, gochujang, honey, mirin, chili flakes, and black pepper. Set aside for later use.
Place the udon noodles in a large bowl and cover with hot water. Let them sit for several minutes until loosened and easy to separate. Drain well and set aside.
Heat half the vegetable oil in a large skillet or wok over medium heat. Add the marinated shrimp and sear for 5 to 8 minutes, flipping halfway through, until pink, opaque, and fully cooked. Transfer the shrimp to a plate and keep warm.
Add the remaining oil to the same pan. Toss in the minced garlic and the white parts of the green onions. Stir-fry briefly until aromatic, about 30 seconds.
Add the cabbage, carrots, mushrooms, and bok choy stems to the pan. Stir-fry for a few minutes until the vegetables are tender-crisp and beginning to soften.
Now, add the drained udon noodles to the pan along with the cooked shrimp, bok choy leaves, green parts of the green onions, and the prepared stir fry sauce. Toss everything together, making sure the sauce coats the noodles and vegetables evenly. Stir-fry for another 2 to 3 minutes until everything is heated through and well combined.
Serve hot and enjoy a hearty, flavorful stir-fry packed with bold, savory notes and satisfying textures.