Place potatoes in a pot and covered with water. Cover pot with lid and bring water to a boil. Salt boiling water and potatoes. Leave lid off pot and simmer at rolling boil until tender, 8 to 10 minutes.
While potatoes cook, combine meat, Worcestershire, onion and steak seasoning or salt and pepper. Form 2 large, oval patties, 1-inch thick.
Preheat large nonstick skillet over medium high heat. Add a tablespoon of extra-virgin olive oil and the meat patties to a hot pan. Cook meat 6 minutes on each side until meat is evenly caramelized on the outside and juices run clear. Remove meat and cover with loose tin foil to keep warm. Add 1 more turn of the pan extra-virgin olive oil and butter to the pan, then the mushrooms. Season mushrooms with salt and pepper and saute mushrooms until tender, 3 to 5 minutes.
While mushrooms cook, squeeze defrosted spinach dry by wringing it out in a kitchen towel. To a small skillet, add butter and cream and heat to a bubble over moderate heat. add spinach and salt and pepper. Cook until spinach thickens with cream, 3 to 5 minutes.
To mushrooms, add a sprinkle of flour to the pan and cook 2 minutes more. Whisk in stock and thicken 1 minute.
While sauce thickens, drain potatoes and return to hot pot. Smash potatoes with a little half-and- half or cream and garlic and herb cheese. Smash and incorporate chives. Add salt and pepper, to your taste.
To serve, pour gravy over Salisbury steak. Serve potatoes and creamed spinach alongside the steaks. Now that's a TV dinner, DELUXE!