Boil water in a large pot and cook noodles according to package instructions, about 7-10 minutes. Drain and toss with vegetable oil.

Heat vegetable oil in a skillet over medium-high heat. Brown the ground beef for 5-7 minutes until cooked through.

Add minced garlic and grated ginger to the skillet, sauté for about 1 minute until fragrant.

In a bowl, whisk together soy sauce, brown sugar, and water until smooth. Add red pepper flakes if desired.

Pour the sauce over the beef in the skillet and let it simmer for 2-3 minutes to thicken.

Mix cornstarch slurry with water and add gradually to the skillet, stirring until the sauce thickens, about 1-2 minutes.

Add the cooked noodles, tossing to coat everything in the sauce, and stir-fry for another 1-2 minutes.

Remove from heat, drizzle sesame oil, and mix in half of the green onions. Serve garnished with the rest.