In a mixing bowl, combine the chopped green olives, black olives, minced garlic, oregano, olive oil, red wine vinegar, salt, and pepper. This is your olive salad. Mix thoroughly and let it sit for 5–10 minutes to allow the flavors to meld.
Slice the Italian bread in half horizontally. If desired, lightly toast the insides of each half on a skillet for 2–3 minutes until golden.
On the bottom half of the bread, layer the sliced mortadella, salami, ham, and provolone cheese. You can adjust the order based on your preference.
Once your olive salad is ready, spread it generously over the cheese layer. Make sure to include some of the olive oil marinade from the salad.
Place the top half of the bread on the sandwich. Press down gently to compress the layers slightly, ensuring that all ingredients adhere together.
If desired, wrap the sandwich tightly in plastic wrap and refrigerate for at least 30 minutes to allow the flavors to meld further. You can also use a sandwich press or a heavy skillet to press down on the sandwich for a few minutes before serving.
To serve, slice the sandwich into quarters and enjoy!