Mix the beef together with 1 clove of the garlic, 1 teaspoon sugar, ¼ teaspoon ground black pepper, 1 tablespoon soy sauce, and 1 teaspoon of sesame oil.
Prepare the vegetables, and set aside. Cook the noodles for 7 minutes in a large pot of boiling water. Strain and cut with scissors so that they’re a little shorter. Add 1 tablespoon sesame oil, 1 tablespoon soy sauce, and 2 teaspoons sugar to the noodles. Toss thoroughly.
Heat up a skillet over medium high heat. Stir-fry the onion and carrot with 1 tablespoon of vegetable oil until tender, but still a little crunchy. Transfer to a large mixing bowl. Add another tablespoon of oil to the pan, and add the mushrooms. Cook until caramelized, and transfer to the mixing bowl along with the onion and carrot. Add another tablespoon of oil to the pan, and cook the red peppers until tender. Add in the spinach, scallions, and the remaining garlic. Cook the entire mixture until the scallions and spinach are wilted. Transfer to the mixing bowl with the other vegetables.
Turn up your heat to high, and add the beef to the pan. Stir-fry for a couple minutes until the beef is no longer pink. Transfer the noodles and the beef to the mixing bowl, along with the sesame seeds.
Add 3 teaspoons sugar, ½ teaspoon ground black pepper, 2 1/2 tablespoons soy sauce, and 1 tablespoon of sesame oil to the mixing bowl full of ingredients. Toss to combine all the ingredients together, and serve.