Mix the ground beef, ⅓ cup French onion soup, breadcrumbs, egg, parsley, salt and pepper in a medium-sized bowl until well combined, and divide the mixture into 6 patties.
Make the gravy: in a small bowl combine the rest of the soup with the ketchup, Worcestershire sauce, flour, mustard powder, garlic powder, and water until smooth.
In a large skillet, heat the olive oil and brown the patties on both sides.
Pour the prepared gravy over the patties, place the sliced mushrooms on top, and cook for 20 minutes with the lid on. The patties should be cooked through and the gravy thick.