To prepare panzanella, cut the bread into rough chunks and place them in a large bowl. Add just enough water (and a little vinegar if you want) to dampen the bread and leave it to rest for 20-30 minutes. In the meantime, clean and trim the vegetables and slice the onion (soak the sliced onion in a bowl of cold water to soften the flavour a little if you like), and cut the cucumber and tomatoes into chunks. 

Hand squeeze the bread - it should not be excessively wet. Mix the tomatoes, cucumber and onion together in a large bowl. 

Add the pieces of bread and the hand-torn basil leaves. Dress with plenty of oil, the 40 g of vinegar, salt and a touch of pepper. 

Mix well and leave the panzanella to rest for a couple of hours before serving.