In a small skillet over medium-low heat, add 3 tablespoons olive oil, the butter, garlic, red pepper flakes, and salt and pepper, to taste. Cook to infuse the butter and oil with the garlic, about 4 minutes.
Add the cubed bread to a large bowl, pour the butter and garlic mixture over the bread and toss to coat. Transfer to a sheet tray and bake until crisp, about 10 minutes. Remove from the oven and let cool.
In a small bowl whisk together the remaining olive oil and red wine vinegar and set aside.
In a large serving bowl, combine the tomatoes, olives, mozzarella, croutons, basil, and the oil and vinegar mixture. Gently toss to coat all the tomatoes and croutons. Let the salad sit for 10 minutes before serving.