Make the stir-fry sauce: In a small bowl, whisk together soy sauce, hoisin sauce, and brown sugar. Set aside.

Prepare the noodles: Blanch fresh udon noodles in boiling water for 1–2 minutes to loosen.. Drain and rinse under cold water. Set aside. If you prefer, you can skip this step and gently separate the noodles by hand. NOTE: If using dried noodles, cook according to package instructions until al dente.

Sauté aromatics: Heat the oil in a large wok or deep pan over high heat. Add the shallots and cook for 1–2 minutes until soft and translucent. Stir in garlic and ginger, and sauté briefly until fragrant.

Cook the mushrooms: Add the sliced mushrooms and stir-fry for 5–6 minutes, stirring occasionally, until they've softened and most of the moisture has evaporated.

Add greens: Stir in the pak choi stems first, cook for 1 minute. Then add the leaves and cook for another 30 seconds until just wilted.

Bring it all together: Add the noodles, green onions, and stir-fry sauce to the pan. Toss everything together and stir-fry for 1–2 minutes until heated through and evenly coated with sauce.

Garnish and serve: Sprinkle with sesame seeds. Serve hot. Optional: finish with a drizzle of sirachi chili sauce or chili oil for extra flavor. Enjoy!