Preheat the oven to 375F. Arrange the bacon on a broiler pan or rack set over a rimmed baking sheet. Bake until crisp, 15-17 minutes.
Preheat a cast-iron or other heavy skillet over medium-high heat. In a small bowl, stir together the blue cheese and butter.
In a large bowl, combine the ground meat, Worcestershire, parsley, some salt and lots of pepper. Form into four patties, thinner at the center and thicker at the edges for even cooking.
Drizzle the hot pan with EVOO. Add the patties and cook, turning once, 8 minutes for medium-rare beef or 12 minutes for turkey.
Season the tomato slices with salt and pepper. Dress the avocado with the lemon juice. Place the burgers on the bun bottoms and slather with the blue cheese butter. Layer with some bacon, lettuce, tomato, avocado, onion and bun tops.