Slice beef into 1/4-inch strips, Put them in a shallow mixing bowl and add soy sauce, sugar, 2 tsp of minced garlic, sesame oil, pepper, and rice wine. Mix well and set aside.
To amke the japchae sauce, combine all the japchae sauce (except sesame seeds) in a small mixing bowl; set aside.
Heat 1 tablespoon of oil in a large skillet or wok over medium heat. Add the onion and the rest of garlic and stir-fry 1 minute. Add the red pepper and continue to cook for another minute. Add the mushroom and pinches salt, cook until the mushroom is soft, adding more oil if necessary. Add the asparagus and pinch salt and stir-fry until asparagus is crisp tender, about 2 minutes. Transfer the veggies on a large platter and spread them out. Set aside.
Bring a pot of water to boil and cook the noodles according to the package direction.
Meanwhile heat a little bit of oil on a skillet again and cook the beef until browned. Place the beef on top of the veggies in a platter; set aside to cool.
When the noodle is cooked, rinse under the cold water to remove the excess starch. Cut noodles with a pair of scissor if desired. Strain the noodles well.
Heat the rest of oil in a skillet over medium heat and add the noodles and toss for 30 seconds. Pour the japchae sauce over noodles and coat them well, about 1 minute. Remove the skillet from the heat and add the veggies and beef, toss well. Serve warm or at room temperature.