Prepare the hamburger steaks: In a large bowl, combine the ground beef, breadcrumbs, beaten egg, chopped onion, garlic powder, Worcestershire sauce, salt, and pepper. Mix until well combined, then shape the mixture into 4-5 patties.
Cook the steaks: Heat a large skillet over medium heat. Add the hamburger patties to the skillet and cook for about 4-5 minutes on each side, or until they are browned and cooked through. Remove the patties from the skillet and set them aside.
Make the gravy: In the same skillet, melt the butter over medium heat. Add the sliced mushrooms (if using) and chopped onion, and sauté for about 3-4 minutes, or until the onions are soft and the mushrooms are lightly browned.
Thicken the gravy: Sprinkle the flour over the onion and mushroom mixture, stirring continuously for about 1 minute to cook off the raw flour taste. Gradually pour in the beef broth while stirring, ensuring no lumps form. Continue to stir until the gravy thickens, about 3-5 minutes.
Add Worcestershire sauce and season: Stir in the Worcestershire sauce, and season the gravy with salt and pepper to taste. Adjust seasoning if necessary.
Smother the steaks: Return the cooked hamburger steaks to the skillet, spooning the gravy over them. Let them simmer in the gravy for another 5 minutes, allowing the flavors to meld together.
Serve: Serve the savory smothered hamburger steaks with mashed potatoes, rice, or your favorite side dish. Enjoy this comforting meal!