Prepare the Bread: Place the bread slices on a cutting board. Using a pumpkin-shaped cookie cutter or a sharp knife, carefully cut each slice into a pumpkin shape. Save the bread scraps for breadcrumbs or another recipe.
Add the Cheese: Place the cheddar and mozzarella over four pumpkin-shaped bread slices, leaving a small border around the edges. Sprinkle lightly with garlic powder and black pepper.
Assemble the Sandwiches: Place the remaining pumpkin-shaped bread slices over the cheese. Press gently around the edges to help hold the sandwiches together. If desired, carefully score a few shallow pumpkin-ridge lines into the top of each sandwich.
Butter the Bread: Spread softened butter evenly over the outside of each sandwich. Make sure the butter reaches most of the surface for an evenly golden and crispy crust.
Cook the First Side: Heat a large skillet over medium-low heat. Place the sandwiches butter-side down and cook for about 4–5 minutes, or until the bottoms are golden brown and crisp.
Flip and Finish Cooking: Carefully flip each sandwich with a wide spatula. Cook the other side for another 4–5 minutes, lowering the heat if needed, until golden brown and the cheese is completely melted.
Add the Pumpkin Stem: Transfer the grilled cheese sandwiches to a cutting board and let them rest for about 2 minutes. Add a small piece of fresh parsley to the top of each sandwich to resemble a pumpkin stem.
Slice and Serve: Slice the sandwiches in half if desired and serve immediately while the bread is crisp and the cheese is warm and gooey.