In a mixing bowl, combine the ground beef, breadcrumbs, egg, garlic powder, onion powder, salt, black pepper, and Worcestershire sauce. Mix until just combined. Shape into 4 equal patties.
Heat the vegetable oil in a large skillet over medium-high heat. Once hot, add the patties and cook for about 4-5 minutes on each side until browned and cooked through. Remove the patties from the skillet and set aside.
In the same skillet, add the sliced onions and sauté until soft and caramelized, about 5-7 minutes.
Sprinkle the flour over the onions and stir to combine; cook for 1-2 minutes.
Slowly add the beef broth, stirring continuously to avoid lumps. Add the soy sauce and bring to a simmer. Cook for an additional 5 minutes or until the gravy thickens.
Return the hamburger patties to the skillet, nestling them in the gravy. Simmer for 5 more minutes to heat through and allow the flavors to meld.
Serve the smothered hamburger steaks topped with the onion gravy, and garnish with chopped parsley if desired.