Porchetta, a seasoned boneless pork roast, can be found in the deli case, but you can use any cold cuts here. For a make-ahead twist, wrap the sandwich tightly with plastic wrap, and chill under the weight of a heavy cast-iron skillet up to 8 hours.
Stir together first 8 ingredients. Add salt and pepper to taste. Cut ciabatta loaf in half lengthwise. Scoop out soft bread from both halves, leaving a 1/2-inch-thick shell. (Reserve soft center of loaf for another use, if desired.)
Spoon olive mixture into bottom half of bread loaf, and spread mustard on top half. Layer meats and cheese slices on top of olive mixture. Top with onions and arugula. Cover with bread top, mustard side down. Cut loaf into wedges or slices.
Note: 1 cup jarred Italian olive salad, drained, may be substituted for olive mixture.