In a large bowl, combine the chopped tomatoes, torn basil leaves, and sliced red onion.
In a small bowl, whisk together the olive oil, balsamic vinegar, salt, black pepper, and garlic powder (if using).
Pour the dressing over the tomato mixture and gently toss to combine, ensuring the tomatoes and basil are well coated.
If using mozzarella balls, add them to the salad and gently mix.
Let the salad sit for about 10-15 minutes at room temperature to allow the flavors to meld.
Serve immediately or refrigerate for up to 1 hour before serving for a chilled option.