In a large bowl, whisk together all ingredients for the marinade.
Add the shredded beef into the bowl and use your hands to coat the shreds with the marinade. Make sure to pull apart the layers of meat for full marinade coverage. Allow to marinate for at least 1 hour, or up to 12. When you’re ready to cook the meat, make sure it is room temperature.
Grill: Preheat the grill too high. Lay meat onto the grill in a single layer and cook for 4-5 minutes before turning—in total, cook for about 8 minutes. Allow meat to char slightly for a smokey flavor and delicious caramelization. Stovetop: Cook on a stove top high heat for the same time, for 4-5 minutes, turning until the meat is cooked through, for about 8 minutes.
Remove meat from the grill or stovetop and allow it to rest for 10 minutes.
Next, cook noodles according to package directions. Drain and set aside.
Make the beef noodles: In an extra large skillet, add the oil with the already cooked shredded cooked beef, plus the minced garlic and sauté for about 1 minute until fragrant.
Stir in soy sauce, brown sugar, beef broth, and red pepper flakes. Let it simmer for 2-3 minutes until the sauce thickens slightly.
Add cooked noodles to the skillet, tossing to coat them in the sauce. Stir in sliced green onions and cook for another minute. Garnish with sesame seeds before serving.