How to Make It
Make the olive relish: Combine giardiniera, olives, bell peppers, parsley, capers, and garlic in a food processor. Pulse until finely chopped. Place mixture in a bowl; stir in oil and vinegar. Let stand 1 hour; cover and chill up to 2 days.
Make the muffuletta: Cut bread in half horizontally. Spread half of olive relish over bottom half of bread; top with half of cheese, all of the meats, and remaining cheese. Spread remaining olive relish on top half of bread, and top sandwich. Wrap entire sandwich tightly in plastic wrap. Refrigerate 1 to 2 hours. Cut into 8 wedges.