Prepare the Olive Salad: In a medium bowl, combine green olives, black olives, giardiniera, garlic, capers, olive oil, red wine vinegar, oregano, and black pepper. Mix well and set aside.
Assemble the Sandwich: Slice the bread in half horizontally. Hollow out some of the soft interior to make room for the fillings.
Layer the Ingredients: Spread half of the olive salad on the bottom half of the bread. Layer the mortadella, salami, ham, and provolone cheese on top. Finish with the remaining olive salad.
Close and Press: Place the top half of the bread over the fillings. Wrap the sandwich tightly in plastic wrap and let it sit for at least 1 hour to allow the flavors to meld.
Serve: Slice the sandwich into wedges and enjoy!