Add beef for 10 minutes in the freezer (it will be easier to cut it later). Wash broccoli and cut into smaller pieces (use only florets). Wash them and set a side.
Prepare beef marinate: in a bowl mix garlic, soy sauce and oyster sauce. Set it aside.
Take beef out of the freezer and cut into smaller lengthwise pieces (slices should be thin).
Pour marinate over the beef, add cornstarch, mix well and let it marinate for at least 30 minutes.
Prepare the sauce: in a bowl mix soy sauce, oyster sauce, ketchup, garlic, brown sugar and set it aside.
Heat the pan to a bit higher than medium heat, add a teaspoon of sunflower oil. Add broccoli florets and cook for about 5 minutes until broccolis become softer. Take broccolis out and set it aside.
Heat the pot to high heat and cook noodles as instructed on the package. Dry out the noodles and set them aside.
Increase pan heat to a bit higher and add beef. Cook for about 4-5 minutes, until the beef becomes slightly brown.
Once beef is done, lower the heat to medium, add broccoli and cook for 2-3 minutes. Then add noodles, sauce and mix everything well.
Serve in a bowl and sprinkle with toasted sesame seeds.