Mix softened butter with garlic powder and oregano. Spread on one side of each bread slice.
Spread pizza sauce on the unbuttered face of two slices, staying half an inch from edges.
Layer half the mozzarella, then pepperoni, then remaining mozzarella on top of the sauce.
Top with remaining bread slices, butter-side facing up.
Cook in a skillet over medium-low heat for 3 to 4 minutes per side until golden and cheese is fully melted. Press gently with spatula during cooking.
Rest for 1 minute before slicing. Serve with marinara dipping sauce.