Prepare the Olive Salad: In a medium mixing bowl, combine the finely chopped green and black olives, sliced roasted red peppers, and chopped giardiniera. Drizzle the mixture with extra virgin olive oil and, if desired, the red wine vinegar for an added zesty flavor. Season the salad with salt and freshly ground black pepper. Stir thoroughly to combine, then let it marinate for at least 30 minutes at room temperature to enhance the flavors.
Slice the Bread: Using a serrated bread knife, carefully slice the round loaf of Sicilian bread in half horizontally to create a top and bottom. Gently hollow out the soft interior of the bread from the center (be careful not to puncture the crust) to create a small cavity. This step is crucial to help prevent the sandwich from becoming soggy.
Layer the Sandwich: Begin building your sandwich by layering the bottom half of the bread. Start with the salami followed by the ham, ensuring an even distribution. Next, add the thin slices of mozzarella and provolone cheese. Finally, spoon the marinated olive salad over the cheese layers, ensuring that it is evenly spread.
Top It Off: Carefully place the top half of the bread back onto the sandwich. Press down gently to compact the layers, allowing the flavors to meld together beautifully.
Wrap and Refrigerate: Tightly wrap the entire sandwich in plastic wrap to keep the moisture in. Place a heavy skillet or a cutting board on top to compress the sandwich further, aiding the melding of flavors. Refrigerate for at least 1 hour, but for an even better flavor profile, leave it overnight.
Serve: When ready to serve, unwrap the sandwich and slice it into wedges or halves for easy sharing. Before serving, garnish with fresh basil leaves on top for a splash of color and freshness.