Prep: Bring a large pot of heavily salted water to a boil. Add 2 cups fusilli pasta and cook until al dente. Drain, add a few ice cubes, and set aside in the colander to cool.
Make the Croutons: Toss sourdough cubes with melted butter and minced garlic. Bake at 375°F (190°C) for 10-12 minutes or until golden and crispy.
In a large bowl, mix diced Campari tomatoes, balsamic vinegar, olive oil, salt, and black pepper. Let sit for 10 minutes to develop flavor.
Add half of the cooled pasta to the bowl and toss gently until coated. Stir in the chopped basil and mozzarella balls, then add the rest of the pasta and toss again.
Top with croutons just before serving. Store in the fridge for up to 3 days.