Prep ingredients per the instructions above.
Mix the oil, vinegar, olives, celery, roasted pepper, garlic, shallots, and oregano in a bowl until fully combined.
Lightly toast the ciabatta. Spoon the olive mixture inside both halves of the ciabatta.
Layer the bottom half of the ciabatta with mortadella, salami, provolone, and ham, and place the top half of the ciabatta over top.
To serve: Cut muffuletta in half and enjoy with carrot sticks, ranch, and sparkling water.