01 - In a medium bowl, combine shredded chicken, Buffalo wing sauce, melted butter, garlic powder, and black pepper. Mix until the chicken is thoroughly coated.
02 - In a separate bowl, combine the shredded cheddar and mozzarella cheeses.
03 - Lay out eight slices of bread. Spread one side of each slice with softened butter. Place four slices, butter-side down, on a clean preparation surface.
04 - Top each of the buttered bread slices with a generous layer of the cheese mixture, followed by a portion of the prepared Buffalo chicken. If using, sprinkle with blue cheese crumbles and chopped green onions.
05 - Add another layer of cheese on top of the chicken mixture. Cap each sandwich with the remaining bread slices, ensuring the buttered side faces upward.
06 - Heat a large skillet or griddle over medium heat. Carefully place the assembled sandwiches onto the heated surface. Cook for 3 to 4 minutes per side, pressing gently with a spatula until the bread is golden brown and the cheese is fully melted.
07 - Remove the grilled sandwiches from the skillet. Let them rest for 1 minute before slicing and serving warm.