Place the ground beef in a large bowl, scatter over the garlic powder, onion powder, salt, black pepper, and ground mustard, then blend lightly with a fork before shaping the mixture into 4 equal patties. The mixture should look evenly seasoned but still loose and textured rather than packed into a dense mass.

Heat a cast iron skillet over medium-high heat, add the patties, and cook the first side untouched for about 4 minutes; flip and cook the other side for 4 minutes more, then transfer the patties to paper towels. Both sides should have a dark brown crust, with browned bits remaining in the skillet for the gravy.

Pour off the skillet grease until about 2 tablespoons remain, cook the sliced onion for about 3 minutes until translucent, then stir in the undiluted onion soup, gravy mix, and water; bring it to a boil, lower it to a simmer, add the Worcestershire sauce, and return the patties to the pan until cooked through. The gravy should bubble gently rather than boil hard, and the patties should feel lightly springy at the center when checked for doneness.