01 - Preheat the oven to 350°F. Alternatively, set a large cast-iron skillet or griddle over medium heat.
02 - Using a serrated knife, slice the entire connected sheet of Hawaiian rolls horizontally in one even cut, keeping the rolls attached. Place the bottom half on a rimmed baking sheet or flat work surface.
03 - Distribute the cheddar and mozzarella slices evenly across the bottom half of the rolls, covering the entire surface edge to edge. Place the top half of the rolls back over the cheese layer.
04 - In a small bowl, combine the softened butter, garlic powder, and chopped parsley. Mix until well incorporated. Evenly spread or brush the butter mixture across the top of the roll slab.
05 - For the oven method: Bake uncovered for 12 to 15 minutes until the cheese has fully melted and the tops are golden brown. For the skillet method: Cut the slab into individual rolls and grill each side for 2 to 3 minutes, pressing lightly, until golden and the cheese is melted throughout.
06 - Remove from heat and allow to rest for 2 to 3 minutes. Separate the rolls along their perforations and serve warm.