Preheat oven to 350°F and line a large baking sheet with parchment paper.
Halve the tomatoes and place in a colander over a large bowl. Sprinkle with salt and pepper, and allow to drain for at least 15 minutes, tossing occasionally. The tomato juices will drain into the bowl, which you’ll use to make the salad dressing.
While the tomatoes drain, toss the bread cubes with 3 tablespoons olive oil in a large bowl to evenly coat them. Place the bread cubes on prepared baking sheet and spread out into one layer. Toast for 15 minutes, or until the bread is golden brown and crisp, but not brown. Remove from the oven and set aside to cool completely.
Remove the colander with the tomatoes from the bowl and set aside. Add the remaining olive oil (5 tablespoons) and red wine vinegar to the tomato juice and whisk constantly until homogenous. Season with salt and pepper.
When you are ready to serve your salad, place the toasted bread, tomatoes, and torn mozzarella in the large bowl with the dressing. Toss to combine, and season with salt and pepper. Allow to sit for 20 minutes to allow the bread to soak up the dressing.