In a large bowl, combine the ground beef, breadcrumbs, milk, egg, garlic powder, onion powder, salt, black pepper, and Worcestershire sauce. Mix until just combined. Form the mixture into 4 equal patties.
Heat the vegetable oil in a large skillet over medium heat. Add the hamburger patties and cook for about 4-5 minutes on each side, or until browned and cooked through. Remove the patties from the skillet and set aside.
In the same skillet, add the sliced onions and cook until they are soft and caramelized, about 8-10 minutes. Sprinkle the flour over the onions and stir to combine, cooking for an additional minute.
Slowly pour in the beef broth and soy sauce, stirring constantly to avoid lumps. Add the thyme and bring the mixture to a simmer. Cook for about 5 minutes, or until the gravy thickens.
Return the hamburger patties to the skillet, spooning the gravy over them. Simmer for an additional 2-3 minutes to heat through.
Serve the hamburger steaks hot, garnished with fresh parsley.