Slice bread horizontally into two equal halves.
Mix olives, giardiniera, peppers, oil, and vinegar.
Add oregano and stir to combine well.
Spread half olive mix on bottom bread.
Layer salami slices over olive mixture.
Add mortadella slices in even layer.
Place ham slices neatly over mortadella.
Add provolone slices to cover meat.
Place mozzarella slices over provolone.
Spread remaining olive mix on top bread.
Close sandwich and press firmly.
Wrap tightly with cling wrap.
Refrigerate sandwich for one hour.
Slice into wedges and serve cold.