Let meat rest to take the chill from the refrigerator.
Preheat 2 nonstick skillets over medium high to high heat.
Place the meat in a bowl and score it into 4 equal sections and form the meat into patties. Season each patty with grill seasoning. Pour a few tablespoons of Worcestershire sauce into a small dish and using a pastry brush, lightly baste the burgers with sauce. Drizzle a touch of oil into the 1 hot skillet and arrange the burgers. Do not move the meat for 2 minutes. Turn and sear the reverse side to caramelize the meat. Lower the heat slightly and cook 5 minutes longer on each side.
Place bacon slices in the other skillet and cook for 3 minutes on each side, until crisp. Drain fat and reserve bacon. Return the skillet to the stove top. Add 2 tablespoons oil, the garlic and mushrooms to the pan. Thinly slice sage leaves, then add to the mushrooms and season with salt and pepper. Saute the garlic and mushrooms 5 minutes until just tender. Deglaze the pan with dry sherry and scrape up the pan drippings.
Pile the mushrooms on top of burgers, then top with bacon and cheese and cover with lid or foil to melt cheese. Transfer burgers to dinner plates. Pass grainy mustard at the table.