In a mixing bowl, combine ground beef, Worcestershire sauce, salt, pepper, onion powder, and garlic powder. Mix until just combined, and form the mixture into 4 equal-sized patties.
Heat 1 tablespoon of vegetable oil in a large skillet over medium-high heat. Once hot, add the hamburger patties and cook for about 4-5 minutes on each side until nicely browned and cooked through. Remove the patties from the skillet and set aside.
In the same skillet, add the remaining tablespoon of oil and the sliced onions. Sauté the onions over medium heat for about 5 minutes or until they are translucent and starting to caramelize.
Sprinkle the flour over the onions and stir well, cooking for about 1 minute. Gradually pour in the beef broth while continuously stirring to prevent lumps.
Bring the gravy to a simmer and cook for about 2-3 minutes until it thickens. Taste and adjust the seasoning if needed.
Return the hamburger patties to the skillet, spooning the gravy over the top of each patty. Cover and cook on low heat for another 5-10 minutes, allowing the flavors to meld.
Serve hot, garnished with fresh parsley if desired.