Boil the noodles: Bring a large pot of salted water to a boil. Cook the noodles according to the package directions until just tender. Drain well, toss with a tiny drop of oil to prevent sticking, and set aside.
Prep the sauce: In a medium bowl, briskly whisk together the low-sodium soy sauce, dark brown sugar, 1/2 cup cold water, and toasted sesame oil until the sugar dissolves. In a separate tiny bowl, mix the cornstarch and 2 tablespoons of cold water until smooth. Set both bowls near the stove.
Brown the meat: Heat a large skillet or wok over medium-high heat. Add the ground beef, spreading it into a flat layer. Let it sear undisturbed for 3 minutes to build a dark crust, then break it apart and cook until no pink remains. Drain excess grease if necessary.
Sizzle the aromatics: Push the cooked meat to one side of the skillet. Add the minced garlic and grated ginger to the empty space. Sizzle for about 30 seconds, stirring constantly so it doesn't burn, then mix it into the beef.
Thicken the glaze: Pour the soy sauce mixture into the skillet. Let it rapidly bubble for 2 minutes. Give your cornstarch slurry a quick stir and pour it into the pan. Watch the liquid instantly transform into a thick, glossy syrup.
Toss and serve: Drop the drained noodles into the skillet. Toss everything together with tongs until every strand is coated in the dark brown sauce. Turn off the heat, stir in the white parts of the sliced green onions, and serve immediately topped with the remaining green onions.