In a large bowl, combine ground beef, breadcrumbs, milk, egg, garlic powder, onion powder, salt, and black pepper. Mix until just combined. Form the mixture into 4 equal patties.

Heat 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 sauté for about 5 minutes, or until they are soft and translucent.

Sprinkle the flour over the onions and stir to combine. Gradually add the beef broth and Worcestershire sauce, stirring constantly until the mixture thickens, about 3-4 minutes.

Return the hamburger patties to the skillet, spooning the gravy over them. Let them simmer in the gravy for an additional 2-3 minutes.

Serve hot, garnished with fresh parsley.