Begin by slicing the chicken thighs into thin, bite-sized strips. Transfer the meat to a bowl and combine with light soy sauce, sesame oil, honey, and a pinch of white pepper. Mix thoroughly to coat, then cover and let the chicken marinate for about 30 minutes to absorb the flavors.
Bring a large pot of water to a rapid boil and cook the egg noodles for less than one minute—just until tender. Immediately drain and transfer the noodles to a bowl of cold water to stop the cooking process. Once cooled, strain the noodles again, gently separate them with your hands, and pat dry using a clean kitchen towel. Set aside.
Prepare your vegetables by slicing the red bell pepper and brown onion into thin strips. Cut the broccolini into 1½-inch pieces, and trim and slice the spring onions, keeping the white and green parts separate.
For the sauce, finely mince the garlic and add it to a small bowl. Stir in oyster sauce, light soy sauce, dark soy sauce, sesame oil, and water. Mix well until smooth and set aside for later use.
Heat a wok or large skillet over high heat and add 1 tablespoon of vegetable oil. When the oil is shimmering hot, add the marinated chicken and stir-fry quickly, turning often until browned and fully cooked through. Remove from the pan and set aside.
Wipe the wok clean using water and a cloth. Add another tablespoon of oil and increase the heat. Once hot, add the noodles and stir-fry until they develop a light golden color and slightly crispy edges. Remove and set aside.
Now, stir-fry the vegetables. Start with the red bell pepper, cooking for 15 to 30 seconds depending on your heat level. Follow with the brown onion, broccolini, and chopped spring onions, allowing each to soften slightly before adding the next. Return the cooked chicken and noodles to the wok along with the bean sprouts. Toss everything together over high heat.
Finally, crank up the heat and pour in the prepared sauce. Stir-fry everything vigorously for a few more seconds to evenly coat all ingredients. Serve immediately while hot and fragrant.