In a large bowl, combine the ground beef, grated onions, salt, crushed dried marjoram, and pepper.
Mix gently until just combined, being careful not to overwork the meat.
Divide the mixture into 6 equal portions and shape each into an oval patty about 3/4-inch thick.
Position the oven rack about 3 inches from the heat source and preheat the broiler.
Place the patties on a broiler pan and broil for 3 to 4 minutes on the first side.
Flip the patties and broil for about 4 minutes on the second side until cooked to desired doneness.
Prepare the mushroom gravy according to the package directions while the patties are cooking.
Stir the drained sliced mushrooms and red wine into the prepared gravy and heat through.
Transfer the Salisbury steaks to a serving platter and spoon the mushroom gravy over the top before serving.