**Prep the Sandwiches:** Spread butter on one side of each slice of bread. On the unbuttered side, spread a thin layer of pizza sauce.
**Assemble the Sandwich:** Place 1/4 cup of shredded mozzarella on one slice of bread, add 4 slices of pepperoni, and sprinkle with a little grated Parmesan cheese. Top with another 1/4 cup of mozzarella and sprinkle with dried oregano (if using). Place the second slice of bread on top, buttered side facing out. Repeat for the second sandwich.
**Grill the Sandwiches:** Heat a skillet or griddle over medium heat. Place the sandwiches in the skillet and cook for 3-4 minutes per side, pressing down gently with a spatula to ensure even cooking and melting. Flip carefully to avoid the filling spilling out.
**Serve:** Once both sides are golden brown and the cheese has melted, remove from the skillet and cut the sandwich in half. Serve immediately with a side of pizza sauce for dipping.