Boil noodles according to package instructions. Drain, rinse, and set aside.
In a large skillet over medium-high heat, cook the ground beef until browned and fully cooked. Drain excess fat if needed.
Push the beef to one side. Add sesame oil, garlic, and ginger to the pan and sauté until fragrant (about 1 minute). Stir everything together.
Stir in soy sauce, brown sugar, hoisin sauce (if using), and red pepper flakes. Simmer for 2–3 minutes.
Add the cornstarch slurry and cook until the sauce thickens slightly, about 1 minute.
Add cooked noodles to the pan and toss well to coat with the sauce. Let everything heat through, about 2–3 minutes.
Top with green onions and sesame seeds. Serve hot.