Combine the white parts of green onions, red chile pepper, green chile pepper, and garlic in a large bowl.

Add dark soy sauce, 3 tablespoons of walnut oil, and brown sugar to the bowl.

Mix the marinade well.

Add beef to the marinade, cover, and refrigerate for at least 15 minutes, or up to 24 hours.

Bring a large pot of salted water to a boil.

Add egg noodles and cook until softened but still firm, about 2-3 minutes.

Drain the noodles.

Cook spinach in a separate pot of boiling, lightly salted water until wilted, about 3-5 minutes.

Drain the spinach and set aside.

Heat 1 teaspoon of walnut oil in a wok.

Add the green parts of the green onions, bell pepper, snow peas, baby corn, and 1/2 teaspoon of soy sauce.

Stir-fry until lightly browned but still crisp, about 2-3 minutes.

Remove the vegetables from the wok.

Stir-fry noodles with 1 teaspoon of oil and 1/2 teaspoon of soy sauce in the same wok until crisp, about 1-2 minutes.

Transfer the noodles to a plate.

Heat 1 teaspoon of oil in the wok.

Stir-fry the marinated beef and some sesame seeds in batches until fully cooked, about 3-4 minutes.

Add the cooked vegetables back to the wok.

Stir-fry until heated through, about 2 minutes.

Place a layer of drained spinach over the noodles.

Pour the stir-fry mixture on top of the spinach and noodles.