In a bowl, combine beef with half of the minced garlic, 1 tsp sugar, 2 tsp soy sauce, 1 tsp sesame oil, and 1/4 tsp ground black pepper. Stir to combine, cover, and chill in fridge.
In a large nonstick pan, add 2 TB olive oil over medium heat. Once oil is hot, add onion, carrots, shitake mushrooms, and a pinch of salt (1/8 tsp.) Cover and stir over medium heat about 3 minutes or until onion is translucent. Add white mushrooms and pinch of salt. Stir for 2 minutes or until mushrooms just turn soft. Add spinach and stir jut until wilted. Transfer mixture to a very large bowl, cover, and keep warm.
Bring a large pot of salted water to boil.
Meanwhile, in the same nonstick pan (now empty,) add 1 TB olive oil, beef, and green onions over medium heat. Stir until beef is no longer pink. Add beef mixture to the large bowl of veggies and cover.
Place noodles into the large pot of boiling water, stirring often, 7-8 minutes or just until noodles are soft and chewy. Drain, rinse briefly with cold water, draining well. Using kitchen shears, make a few cuts through the noodles so they aren’t as long. Place noodles back in empty pot. Add 3 tsp sugar, 2 tsp soy sauce, and 4 tsp sesame oil. Toss well to combine.
Mix together the noodles and the beef/veggie mixture (either in large bowl or large pot.) Add remaining garlic, sugar, soy sauce, and sesame oil. Add salt/pepper to taste. Toss well by hand. Sprinkle on toasted sesame seeds and serve warm or at room temp.