In a large bowl toss the onions, garlic, coriander, salt and peppers. Add and mix well the lemon juice, brown sugar and soy sauce. Place the steak in a dish big enough to allow the meat to lie flat and pour the marinade over the meat. Cover and marinate overnight.
Remove meat from marinade. You will be reusing the marinade. I suggest that you boil the marinade for 10 minutes to remove any unsavory juices left by the raw meat. Set aside and allow to cool.
Place the meat on a broiler pan or rack about 8 inches from the broiler flame. Broil for about 7 minutes. Turn the meat and pour the remainder of the cooled marinade over the top of the meat and broil another 7 minutes. The steak should be cooked to a medium. If you have a different preference for the doneness of your steak, adjust your cooking time accordingly.
When steak is cooked, let it sit loosely covered with foil for about 15 minutes. Cut in strips against the grain and serve.
Au Gratin potatoes are a great accompaniment to this broiled steak recipe. They can be cooked in the oven ahead of time(they stay warm for some time after leaving the oven). Add a tomato salad with garlic, oregano and red wine vinegar and you're good to go.