Slice the round Italian bread in half horizontally. Hollow out some of the bread from the top and bottom to create space for the fillings.
In a small bowl, mix together the olive oil, green olives, black olives, roasted red peppers, giardiniera, oregano, and garlic powder to create the olive salad.
Drizzle some olive oil on the inside of both halves of the bread. Spread half of the olive salad evenly on the bottom half of the bread.
Layer the salami, ham, mortadella, provolone, and mozzarella on top of the olive salad.
Spread the remaining olive salad on top of the cheese layer, then place the top half of the bread on the sandwich.
Wrap the sandwich tightly in plastic wrap and place a heavy skillet or plate on top to press it down. Refrigerate for at least 1 hour, or overnight for best flavor.
When ready to serve, unwrap the sandwich, slice into wedges, and enjoy.