Panzanella was based on onions, not tomatoes, until the 20th century.

Modern panzanella is generally made of stale bread soaked in water and squeezed dry, red onions, tomatoes, olive oil, vinegar, salt, and pepper.
 Cucumbers and basil are often added.

Other ingredients—lettuce, olives, mozzarella, white wine, capers, anchovies, celery, carrots, red wine, tuna, parsley, boiled eggs, mint, bell peppers, lemon juice, and garlic—are sometimes used, but Florentine traditionalists disapprove of them.
Panzanella was based on onions, not tomatoes, until the 20th century.
Modern panzanella is generally made of stale bread soaked in water and squeezed dry, red onions, tomatoes, olive oil, vinegar, salt, and pepper.  Cucumbers and basil are often added.
Other ingredients—lettuce, olives, mozzarella, white wine, capers, anchovies, celery, carrots, red wine, tuna, parsley, boiled eggs, mint, bell peppers, lemon juice, and garlic—are sometimes used, but Florentine traditionalists disapprove of them.
Panzanella