Slice flank steak against the grain on a 45-degree angle into ¼-inch thin strips. Transfer beef strips to a large bowl. Tip: to thinly cut the beef easily, freeze the flank steak for 20-30 minutes fully exposed to the cold air and cut with a sharp knife.
Add your beef marinade ingredients into the large bowl with the beef. Mix with tongs or clean hands and then pack the beef into a ball so that the marinade can soak into the meat. Set aside to marinate for 15 minutes.
In another large bowl, combine together satay sauce ingredients as listed and mix well or if you have a blender or food processor, use this to blend the satay sauce ingredients until smooth. Set aside.
Heat vegetable oil in a large pan on medium-heat and fry marinated beef. Fry until the edges are brown and the meat is 75% cooked, about 5 minutes.
Then add in satay sauce and toss beef in it. Cook for 1-2 minutes until beef is cooked through and no longer red. Transfer to a plate and set aside.
In a large pot filled with enough water, bring to a boil on medium-high heat. Boil rice vermicelli noodles for a couple of minutes loosened and softer, about 2-3 minutes. Strain immediately. Rinse noodles with cold running water and strain again. Divide your noodles into 5 bowls.
Divide cooked satay beef and place on top of cooked noodles.
In a large pot, combine chicken broth, oyster sauce, regular soy sauce and sesame oil. Bring to a boil on medium-high heat. Once it comes to a boil, divide and pour the soup over the noodles and enjoy hot!