Start the rice first if you would like to serve with rice. In a large skillet on medium heat, heat the broccoli (cut into florets) and 2 tbsp water until the broccoli is bright and crisp-tender. If you prefer your broccoli softer you can add a tbsp or 2 more water and let cook covered for a few more minutes to let it steam. Remove broccoli from pan once cooked.
Increase the heat to high and add 1 or 2 Tbsp of oil. Add the beef in a single layer and saute for about 2 minutes per side or until just cooked through. Be sure to pull out a piece and check for doneness. (I like my steak medium rare, but cook to your preference!)
Add the sauce (that the beef was marinated in), reduce heat and let simmer for 3 or 5 minutes. If you chose to add the corn starch, the sauce will thicken.
Add the broccoli back into the pan and add in water by the Tbsp if a thinner sauce is desired.
Serve over rice!