Cook the rice noodles according to package instructions. Drain and set aside.
In a small bowl, mix together soy sauce, oyster sauce, hoisin sauce, and brown sugar. Set aside.
Heat vegetable oil in a large skillet or wok over medium-high heat. Add the sliced flank steak and cook for about 3-4 minutes until browned. Remove the beef from the skillet and set aside.
In the same skillet, add garlic, ginger, red bell pepper, and snap peas. Stir-fry for about 2-3 minutes until the vegetables are tender-crisp.
Return the beef to the skillet and pour the sauce mixture over the beef and vegetables. Stir to combine and cook for another 2 minutes until everything is heated through and the sauce is sticky.
Add the cooked rice noodles to the skillet and toss everything together until the noodles are well coated with the sauce.
Serve hot, garnished with chopped green onions and sesame seeds.