How to Make It
Preheat the oven to 300°. Spread the bread on a baking sheet and toast for 10 minutes, or until dry but not browned. Let cool, then transfer to a large bowl.
In a small bowl, mix the vinegar with 1 teaspoon of salt until the salt dissolves. Slowly whisk in the olive oil and season with pepper.
Dip your fingers in water and flick them over the bread several times, tossing it with your hands until lightly moistened. Add the tomatoes, cucumber, bell pepper, celery, scallions, mushrooms and dressing and toss until evenly coated. Season the salad with salt and pepper, garnish with the basil and serve.