Prepare the Olive Salad:In a medium bowl, combine the green olives, black olives, roasted red peppers, pickled vegetables, garlic, parsley, olive oil, red wine vinegar, oregano, red pepper flakes, salt, and pepper.Mix well and let it sit for at least 30 minutes to allow the flavors to meld. For the best flavor, prepare the olive salad a day in advance and refrigerate it overnight.
Prepare the Bread:Slice the round loaf of bread horizontally in half. Hollow out some of the soft interior from both the top and bottom halves to create more space for the filling.
Assemble the Sandwich:Spread half of the olive salad over the bottom half of the bread.Layer the salami, ham, mortadella, provolone, and mozzarella over the olive salad.Spread the remaining olive salad over the top half of the bread.
Press the Sandwich:Place the top half of the bread over the layered meats and cheese. Wrap the entire sandwich tightly in plastic wrap.Place a heavy skillet or pan on top of the wrapped sandwich to press it down. Let it sit for at least 1 hour, or up to 4 hours, to allow the flavors to meld and the sandwich to compress.
Serve:Unwrap the sandwich and slice it into wedges or quarters. Serve at room temperature.