Preheat the oven to 205°C.
To prepare the Roast Turkey: toss the herbs and butter into the bowl of a food processor and pulse until green and smooth. Rub the turkey breast with half of the herbed butter and with salt and pepper. Place the turkey on a rack in a roasting pan and put in the oven. Let the turkey cook for 1 hour, basting every 20 minutes with the butter and pan juices. The turkey is done when it reaches an internal temperature of 165 degrees F. Let rest for 15 minutes on the cutting board.
To assemble the sandwich: spread a thin layer of the remaining butter on 1 piece of the bread. Place 1 slice of the cheese and several slices of the turkey breast on unbuttered side of the bread. Peel and slice the avocado, toss with the lemon juice, olive oil, salt and pepper. Add avocado slices, crispy bacon slices, lettuce and another slice of fontina cheese to the top of that. Sprinkle again with salt and pepper. Slather the remaining piece of bread with the butter and place on unbuttered side out, on top of the bacon.
Heat a cast-iron or other heavy skillet over medium-low heat. Add 1 tablespoon of butter and let it melt, swirling the pan around to coat. Put the sandwich in the pan and weigh it down with a heavy pot or can (or wrap an ordinary brick in aluminum foil and set it on top to compress the sandwich.) Toast for 1 minute, turn the sandwich over before the bread begins to burn. Repeat with remaining sandwiches. Cut the sandwiches in half and serve.