Preheat the oven to 350 degrees. Bake the bacon on a broiler pan until crisp, 15 minutes. Preheat the broiler.
In a bowl, combine the beef, shallot and parsley; season with salt and pepper. Form into 4 patties.
In a nonstick skillet, heat a drizzle of EVOO over high heat. Add the patties and cook for 3 minutes on each side for medium-rare.
In a large saucepan, melt the butter over medium heat. Whisk in the flour and cook until light brown, 3 minutes. Stir in the Worcestershire sauce, mustard and hot sauce. Whisk in the stout and cook until thickened, 1 to 2 minutes. Lower the heat and stir in the cheese until smooth.
Arrange the pumpernickel slices on a baking sheet and toast both sides. Pour the sauce over the toasts; broil until the cheese is bubbly, about 2 minutes. Place a patty on each of 4 slices, cover each with a handful of watercress, crisscross with 2 bacon slices and top with a slice of tomato; season with salt and pepper. Cover with the remaining toasts, cheesy side down. Serve with a pile of potato chips.