In a large bowl, toss the ciabatta pieces with ¼ cup olive oil, ½-1 Tablespoon salt, and ¼ teaspoon pepper. Spread out on a baking tray and bake until crispy and lightly browned, about 10-15 minutes. Remove from the oven, transfer to a plate, and allow to cool completely.
Meanwhile, make the vinaigrette. In a small bowl, whisk together ½ cup olive oil, red wine vinegar, Dijon mustard, garlic, ½ teaspoon salt, and ⅛ teaspoon pepper until well combined and emulsified. Set aside.
Halve the cherry tomatoes, thinly slice the red onion, dice the cucumbers, finely chop the basil leaves, and cut the mozzarella.
In a large bowl, combine tomatoes**, red onion, cucumbers, and basil. Add the mozzarella cheese. Add the cooled bread and drizzle with the vinaigrette and gently toss to ensure all the ingredients are evenly coated.
Allow the salad to rest for about 30 minutes at room temperature to let the bread soak up the dressing and the flavors to meld together.
Check the seasoning and adjust with more salt and pepper if needed. Drizzle with a little more olive oil, give the salad a final toss, and serve immediately.
Notes
*Switch out mozzarella with ¼ cup parmesan cheese if desired
**Do not add any juices or seeds that may accumulate while slicing the tomatoes.
Refrigerate leftovers in an airtight container for up to 3 days.