In a mixing bowl, combine ground beef, breadcrumbs, egg, garlic powder, onion powder, salt, pepper, and Worcestershire sauce. Mix until just combined.
Form the mixture into 4 equal-sized patties, pressing them slightly to flatten.
Heat vegetable oil in a large skillet over medium heat. Add the hamburger patties and cook for about 4-5 minutes on each side until browned and cooked through. The internal temperature should reach 160°F (71°C). Remove the patties from the skillet and set aside.
In the same skillet, add the chopped onion and sliced mushrooms. Sauté for about 5 minutes, or until the onions are translucent and the mushrooms are tender.
Sprinkle the flour over the onions and mushrooms, stirring to combine. Gradually add the beef broth, stirring continuously to prevent lumps. Bring the mixture to a simmer and cook for about 5 minutes until thickened.
Return the hamburger patties to the skillet, spooning the gravy over them. Let simmer for another 5 minutes to heat through.
Serve the smothered hamburger steaks hot, garnished with fresh parsley if desired.