Heat 1 tablespoon of the oil in a large skillet over medium-high heat. Add the onion and saute until soft, about 6 minutes. Put 1/2 of the onion in a large bowl and the remainder in another bowl. In the large bowl add the beef, bread crumbs, grill seasoning, Worcestershire sauce and the egg. Mix to combine everything well and form the mixture into 5 oval patties. Heat the remaining tablespoon of oil in the same skillet over medium-high heat. Cook the patties until they are well browned, about 4 to 5 minutes per side. Remove the steaks and pour off all but 2 tablespoons the fat. (The patties will not be cooked through and will finish cooking in the gravy.)
Put the pan back on the heat, add the mushrooms, and cook for 5 minutes. Add the remaining onions, sprinkle in the flour, and cook for 2 minutes. Add the beef broth and bring it to a boil. Return the patties to the pan, reduce the heat to a simmer and cook until the sauce has thickened and the steaks are cooked through, about 10 minutes. Reserve one steak for online round 2 recipe, Beef Empanadas.