Heat a pan up to medium-high. Add oil and wait for 30 seconds. Add marinated steak and cook for 3-4 minutes (stir frequently and separate the ingredients to help make sure they are cooking uniformly).
Add sliced red chili peppers, minced garlic and cook for 1-2 minutes or until fragrant.
Add pre-cooked noodles and sauce. Mix everything together and cook for 2 minutes.
Add green onions, mung bean sprouts and mix everything together until the sauce forms a nice coat over the noodles. Remove the pan from the heat.