Get two pans ready for cooking the beef and the broccoli. I like to cook them separately so they cook evenly.
In a very large saucepan or wok over medium-high heat, add 2 tablespoons of oil and then add the sliced flank steak. Stir well to coat with oil and cook until meat is slightly browned and cook through.
In a separate saute pan, add 1 tablespoon of oil and the broccoli florets. Add 1-2 cups of water and cover to steam broccoli (if you'd like the broccoli softer, add more water, if you'd like it more pan-seared, add less water).
Once beef is cooked through, whisk the sauce well and add to the pan with the beef. Stir well and cook until sauce bubbles and thickens. Once sauce is thickened, add in broccoli. Stir to coat. Make sure it is all evenly coated.
Serve by spooning the beef and broccoli over warm rice. Then top with sesame seeds if desired.Enjoy!