Place the ground beef in a large bowl, scatter over the garlic powder, onion powder, salt, black pepper, and ground mustard, then combine lightly with a fork and shape the mixture into 4 equal patties. Keep the meat loose rather than packed tightly, and press a shallow dip into the center of each patty so it stays flatter in the skillet.

Heat a cast-iron or other heavy skillet over medium-high heat, then sear the patties without moving them for about 4 minutes before turning and cooking the second side for another 4 minutes. Wait for a deep brown crust before flipping, then transfer the patties to paper towels while the skillet retains its browned bits.

Pour off the drippings until about 2 tablespoons remain, cook the sliced onion in the skillet for about 3 minutes, then stir in the undiluted onion soup, gravy mix, and water; bring it to a boil, lower to a simmer, add Worcestershire sauce, and return the patties to the pan. The onions should look translucent and smell sweet before the liquids go in, while the finished gravy should bubble gently around the patties rather than boil hard.