In a saucepan over medium heat, warm the turkey and gravy together until heated through. Season with salt and pepper to taste.
While the turkey and gravy are warming, heat a skillet over medium heat. Spread butter on one side of each slice of bread.
Place two slices of bread, buttered side down, in the skillet. Top each slice with a slice of Swiss cheese, then add the warmed turkey mixture evenly over the cheese.
Place the remaining slices of cheese on top of the turkey, then cover with the other slices of bread, buttered side up.
Cook for about 3-4 minutes or until the bottom is golden brown. Carefully flip the sandwiches and cook for another 3-4 minutes until the other side is golden and the cheese is melted.
Remove from the skillet and cut in half. Serve hot, drizzled with extra gravy if desired, and garnish with chopped parsley.