Combine all of the patty ingredients in a large bowl. Mix together with your hands until it is evenly incorporated. Divide the meat into 4-5 patties, ½” thick. Place on a plate or baking sheet and refrigerate for 30 minutes before cooking.
Meanwhile, combine the beef broth, soy sauce and lemon juice in a measuring cup or bowl and set aside for later.
Heat a nonstick skillet over medium heat. Add your beef patties to the hot skillet. Cook until browned on both sides, about 5 minutes per side. If you prefer medium and not well done patties, cook for a minute less on each side. Remove the cooked patties to a plate and cover with foil to keep warm. Leave the fat in the pan.
Reduce heat to medium low. Add the mushrooms and onions to the beef fat. Cook until softened, about 8 minutes. Remove the onions and mushrooms to the plate with the patties.
Add butter and flour to the warm pan. Whisk together until melted and smooth. Cook for 2-3 minutes, whisking constantly. Add the beef broth mixture to the flour while whisking constantly to avoid lumps. Add salt and pepper to taste.
Add the patties, onions and mushrooms to the gravy. Cook in the gravy until the patties are warmed through, another 3-4 minutes.
Serve over noodles or mashed potatoes.