In a large bowl, combine ground beef, breadcrumbs, milk, egg, garlic powder, onion powder, salt, and black pepper. Mix until just combined, then form 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 patties from the skillet and set aside.

In the same skillet, add sliced onions and cook until softened and caramelized, about 5-7 minutes. Stir occasionally to prevent burning.

Sprinkle flour over the onions and stir to combine. Gradually add beef broth and Worcestershire sauce, stirring constantly until the mixture thickens and is smooth.

Return the hamburger patties to the skillet, spooning the gravy over them. Simmer for an additional 5 minutes to heat through.

Serve hot, garnished with fresh parsley.