In a medium bowl, stir together the soy sauce, oyster sauce, brown sugar, sesame oil, garlic, and rice wine vinegar; set aside. In a large pot, cook rice according to the package directions.
In a large pan over medium-high heat, add the oil and onions, cook until translucent, about 4-5 minutes, stirring continuously. Remove the onions from the pan, cover, and set aside. Add steak into the pan and cook about 4-5 minutes on each side. Add the onions back into the pan with broccoli, cooking about 3-4 minutes. Lower heat to medium, add the sauce, and cook another 3-5 minutes.
Serve beef and broccoli over rice.