Slice the Italian bread in half horizontally and hollow out some of the soft bread inside to make room for the fillings.
In a food processor, combine green olives, black olives, pimento-stuffed olives, and giardiniera. Pulse until coarsely chopped.
Transfer the olive mixture to a bowl and stir in olive oil, vinegar, pepper, garlic powder, and oregano.
Spread half the olive mixture on the bottom half of the bread. Layer with salami, ham, mortadella, provolone, and mozzarella.
Top with the remaining olive mixture and close the sandwich with the top half of the bread.
Wrap the sandwich tightly in plastic wrap and refrigerate for at least 1 hour to let the flavors meld.
Slice into wedges and serve.