Drain the mozzarella then dry with paper towel and cut into thin slices. Slice the tomatoes.
Carefully cut the top of the ciabatta creating a lid. Using your fingers, scrape out the inside of the bread, and brush the inside with olive oil.
Fill with layers of mozzarella, tomato slices and basil leaves, then season and drizzle with some oil. Repeat the layers until the pocket is full.
Put the "lid" on, then wrap the loaf tightly with foil. Put it on a plate and chill in the fridge. Place some weight on the top it, to press down (eg milk cartons, tins).
Few hours later or the next day, remove the loaf from the refrigerator. Just before serving, unwrap and cut 1 inch thick slices.