Begin by cooking the rice noodles according to the package instructions. Drain and set aside.
While the noodles are cooking, slice the flank steak against the grain into thin strips.
Season the steak strips with salt and black pepper.
In a large skillet, heat the olive oil over medium-high heat. Once hot, add the seasoned steak and cook for about 3-4 minutes until browned. Remove from the skillet and set aside.
In the same skillet, melt the unsalted butter over medium heat. Add the minced garlic and sauté for 1-2 minutes until fragrant.
Pour in the beef broth, soy sauce, oyster sauce, and sugar into the skillet. Stir well and bring to a simmer.
Return the cooked steak to the skillet and allow it to simmer in the sauce for 2 minutes.
Add the cooked noodles to the skillet and toss everything together gently to coat the noodles with the sauce.
Cook for an additional 1-2 minutes until everything is heated through.
Serve hot, garnished with chopped green onions and sesame seeds.