In a medium bowl combine the following gravy ingredients: hot water, bouillon cubes, ketchup, Worcestershire sauce, salt, pepper, garlic powder, and cornstarch. Whisk together and then set aside.
In a large mixing bowl combine ground beef, seasoned bread crumbs, ketchup, dry mustard, Worcestershire sauce, crushed beef bouillon cube, salt, pepper, and onion powder. Use hands to mix meat mixture until all combined.
Form meat into 6 equal oval patties.
In a large skillet over medium heat add olive oil. Once the olive oil is heated add the oval patties to the skillet and allow them to cook until browned on one side. Turn over and allow the other side to cook until browned. Once both sides have a nice deep browning on them, and they are cooked through, remove the patties to a paper-lined plate, and set aside. Drain all but 1 tbsp of grease from the pan.
Add onions to the pan and stir well. The bottom of the pan may be very dark and almost have a burned appearance from cooking the hamburgers, which is perfect for this recipe. Allow onions to cook 3-4 minutes. Add garlic powder and butter. Stir and allow to cook for an additional 2 minutes.
Add ½ cup of broth to onions and garlic mixture. Use a spoon or spatula to deglaze the bottom of the pan, making sure to get all of the browned pieces up and into the sauce.
Once the pan is deglazed add mushrooms and stir well. Let cook for 2-3 minutes.
Add the remaining gravy mixture and stir well. Allow to simmer for 5 minutes, stirring often.
Return the patties to the gravy and use a spoon to cover the patties with gravy. Let the patties simmer on low heat for 3-5 minutes, or until warmed through.