Spread butter on one side of each bread slice.
Place a slice of bread, buttered side down, in a skillet over medium heat.
Layer with mozzarella cheese, marinara sauce, pepperoni, garlic powder, oregano, salt, and pepper.
Top with another bread slice, buttered side up.
Cook until the bottom bread slice is golden brown and crispy.
Flip the sandwich and cook the other side until golden brown and cheese is melted.
Remove from the skillet, slice in half, and serve hot.