If you want a crunchy salad, simply dice the bread. If you want the classic salad, soak it in water for at least thirty minutes. Then squeeze it very, very well: you should get a breadcrumb-like consistency.
Cut the tomatoes in small pieces, more or less the same size of the bread.
Peel and thinly slice the onion.
Coarsely chop the basil leaves with your hands.
Place the tomatoes, the onion, and the basil leaves in a large bowl. Season with the vinegar, one to two tablespoons of olive oil, and salt to your taste.
Add the bread and mix well.
Rest fifteen to thirty minutes at room temperature - or in the fridge if it is summer and a hot day.
If you have fresh bread, toast it a few minutes in a very hot oven.
You can add a thinly sliced cucumber, boiled eggs, or canned tuna.