Place butter in a small microwavable dish. Microwave on High until melted, about 25 seconds. Stir in Italian seasoning and garlic powder.
Place 2 slices of bread on a clean work surface. Spread half of butter mixture onto 2 slices of bread; turn bread slices over. Using a spoon, spread 1 tablespoon pizza sauce evenly over each slice, all the way to the edges.
Top each slice with 6 pepperoni slices; scatter evenly with olives, and top each with 1/4 cup mozzarella. Place a plain bread slice on top.
Heat a large skillet over medium-low heat, and place each sandwich in the skillet, butter-side-down down. Cook until golden, about 3 minutes.
Spread remaining seasoned butter over tops of sandwiches. Carefully turn each sandwich over, and cook until cheese is melted and bread is golden, about 3 minutes more. Transfer sandwiches to a plate, cut in half, and serve immediately.