During this time, the Florentine Mannerist painter Bronzino (a contemporary of Michelangelo) penned a sort of recipe-poem about a dish that in all ways resembles a tomato-less panzanella, a dish he compares to a “trip across the stars.” It combined stale bread, arugula, basil, cucumber, and onion. 
The key to this salad is the stale Tuscan bread, which should take up half the salad. It has an incredible consistency when soaked in water: Rather than becoming soggy, it holds its shape and springiness. The best breads to use are country breads that have a good, dark crust on them—if possible, even wood-fired. 

Bronzino's Green Panzanella

Serves 3 to 4

• 4 to 5thick slices of stale, springy country bread with a good crust
• 1small red onion
• 1 to 2tablespoons red wine vinegar, plus more to taste
• 1medium, crunchy cucumber, thinly sliced (you could also peel if you like)
• 1handful arugula, washed and pat dry
• Salt and pepper, to taste
• Extra-virgin olive oil
• 10 to 12basil leaves

1. Pass the slices of bread under running water and let sit in a bowl to soften while you prepare the other ingredients.
2. Slice the red onion very thinly and place in a small bowl. Sprinkle with 1 to 2 tablespoons of the red wine vinegar and cover with cool water. Let sit 10 minutes (this will take some of the edge off the raw onion).
3. When the bread pieces are springy to the touch, tear and crumble the bread in your hands (depending on the type and freshness of your bread, the crusts may be too hard. If so, you may wish to remove them, but some like the chewiness of the crust). If the bread is still too hard, you can sprinkle on some more water, but keep in mind that you’ll be adding vinegar and oil to the salad as well, which the bread will also soak up. If you have added too much water, simply give your bread a squeeze to remove the excess liquid before adding to the salad. Place the bread in a large bowl with the cucumber and arugula.
4. Drain and add the onion to the salad. Season with a good pinch of salt, a few twists of pepper, a healthy dose of olive oil, a splash or two of red wine vinegar, and toss until well combined. Add the basil leaves, torn into pieces just before serving.

https://food52.com/recipes/36335-bronzino-s-green-panzanella