Start by marinating the beef; mix together cornstarch mixture, soy sauce, rice wine or water, salt and pepper in a bowl, add the sliced beef and stir to coat the slices. Let stand for 30 minutes while you prepare the sauce and blanch the broccoli.
Make sauce by mixing the oyster sauce, rice wine or water, soy sauce and chicken broth in a small bowl. Set aside.
Place broccoli in salted boiling water for 2 minutes, remove the broccoli from the boiling water with a large Chinese wire mesh skimmer/strainer and immediately submerge the broccoli into a large bowl filled with ice cubes and cold water. Submerge for 10 seconds. Remove the broccoli with wire mesh skimmer/strainer from the cold water, drain well and set aside.
Heat a large frying pan or wok over high heat until a bead of water sizzles and instantly evaporates upon contact, add oil and swirl to coat pan or wok. Add bell pepper strips, cook for a few minutes. Remove and set aside. Heat pan again and add meat slices, let the beef fry for 1 minute. Flip the beef strips over and add the garlic, sliced green onion, if using, reserved bell pepper strips and fry for 30 seconds to 1 minute.
Pour in sauce, add broccoli and bring to a boil. Pour in dissolved cornstarch in water and cook stirring until sauce boils and thickens, about 30 seconds.
Served this wonderful Beef and Broccoli Stir Fry over Jasmine Rice.