Layer each of four bread slices with a slice of mozzarella, garlic powder, six slices of pepperoni, and a teaspoon of Parmesan cheese. Top with another slice of mozzarella and cover with another slice of bread.
Spread softened butter on the outside of each sandwich.
Heat a skillet over medium heat and place the sandwiches in the skillet.
Cook each side for about 3-4 minutes or until golden brown and the cheese is melted.