Step 1Break the noodles into 6-or 7-inch pieces, then cook them in boiling water until the noodles are translucent and slightly springy when pulled, 4 to 5 minutes. Immediately drain and rinse them thoroughly in cold water.
Step 2Soak the mushrooms in cold water for about 1 hour. Squeeze the liquid from the mushrooms, cut off the stems and discard them. Slice the mushrooms.
Step 3Heat 2 tablespoons of oil in a skillet over high heat. Add the mushrooms, beef, 2 cloves of minced garlic, 1 tablespoon of soy sauce, 1 teaspoon of sesame oil and 1 teaspoon of crushed sesame seeds and cook until the beef is cooked through and no longer pink, about 3 to 4 minutes. Remove from the heat and set aside.
Step 4In boiling water, blanch the spinach. Squeeze the water from the leaves and cut them in half. In a bowl, combine the spinach, the remaining 2 cloves of minced garlic, 1 teaspoon of salt, 1 teaspoon of sesame oil, 1 teaspoon of crushed sesame seeds and mix. Set aside.
Step 5Heat 2 tablespoons of oil in a skillet over high heat. Add the white onions, carrots, green pepper and 1 teaspoon of salt and cook until the onions and peppers start to soften, 3 to 4 minutes. Add the green onions and stir-fry for about a minute more. Remove from the heat and set aside.
Step 6In a large bowl, thoroughly combine the noodles, beef mixture, spinach, onion mixture, 1/2 cup of soy sauce, remaining 2 tablespoons of sesame oil, 1 tablespoon whole toasted sesame seeds and the sugar.
Step 7Serve warm, sprinkled with whole sesame seeds if desired.