This sandwich is packed with fresh flavors that only get better overnight as it compresses. It's a crowd pleaser - who doesn't like mozzarella, fresh pesto, salty prosciutto and intense sun-dried tomatoes? And it makes life easy on the picnic cook - one giant sandwich takes way less time to make than dozens of small ones, and this sandwich gets better if you let it sit overnight!
Incidentally, I recently went to a cocktail party where they served a version of these sandwiches sliced into bite sized cubes (I think they also cut the middle out of the bread to give a better bread to filling ratio). People who'd previously spent half an hour telling everyone about their juice fasts were wolfing them. —MakeThatMakeThis
Make the pesto by putting the basil, pine nuts (toast them first in the oven if you have time) and cheese in a processor. Grate in the garlic, then blend, adding olive oil through the hole in the top to make a thick paste. Season well
Slice the ciabatta lengthwise, spread both cut sides with the pesto, then build up the filling in layers, ham then cheese slices, then sundried tomatoes, more cheese slices etc, seasoning each layer
Sandwich the bread together again, wrap tightly in plastic wrap and put in the fridge with cans on top of it to weight it down (it might balance better to put a baking tray on top, then the cans on the tray). Refrigerate overnight.