Coarsely chop the green olives and black olives so pieces are about 1/4 inch. Add chopped pepperoncini, pickled celery, roasted red peppers, capers and minced garlic to a medium bowl.

Stir in olive oil, red wine vinegar, dried oregano, black pepper and salt until well combined. Taste and adjust seasoning — the mixture should be bright, tangy and slightly salty. Let the olive salad sit at room temperature for at least 15 minutes to meld flavors (or refrigerate up to 24 hours). Drain any excess oil/vinegar if it seems very wet before spreading on rolls.

Bread & Assembly

Prepare spreads

In a small bowl combine mayonnaise and Dijon mustard. Mix until smooth and set aside.

Slice each roll horizontally, keeping top and bottom intact. Lightly butter the cut faces with the mayo-mustard mixture (about 1 tablespoon per roll bottom and 1/2 tablespoon on each top). This creates a barrier and adds flavor.

Place 1 slice provolone on the bottom half of each roll, followed by 2 slices salami folded to fit, 1 slice ham, and 1 slice mortadella (or 2 folded slices if needed). Divide the mozzarella evenly across the 8 bottoms.

Spoon about 2 tablespoons of the prepared olive salad onto the cheese/meat layer of each sandwich. Spread it evenly but avoid overfilling so the sandwich can close cleanly. Top each with the reserved provolone slice (if your provolone is beneath, place it atop the olive salad to help protect bread from moisture). Close sandwiches and press gently.

Finish & Toasting

Preheat a skillet or griddle over medium-low heat (350°F / 175°C on an electric griddle) or preheat an oven to 375°F (190°C) if you prefer oven toasting.

Brush the outside tops and bottoms of each roll lightly with melted butter (about 1/2 teaspoon per surface). Place sandwiches, buttered-side down, on the skillet and weight them with a heavy pan or sandwich press. Cook 3–4 minutes per side until golden and cheese is melty. If using the oven, place sandwiches on a baking sheet and bake 8–10 minutes, flipping once, until golden and heated through.

Remove from heat and let rest 1–2 minutes. If desired, sprinkle chopped parsley over tops for color.