Cut the stem end off the tomatoes and discard. Chop the tomatoes into one inch pieces and place into a large mixing bowl.
Add the diced red onion, minced garlic, and drained capers to the tomatoes in the mixing bowl.
In a small mixing bowl, whisk together olive oil, vinegar, sugar, salt, and pepper. Whisk vigorously until the dressing has emulsified (1-2 minutes).
Pour the dressing over the tomato mixture and toss until completely combined. Cover the bowl with plastic wrap and allow to chill in the fridge for at least one hour before serving.
When serving, garnish each salad with freshly chopped basil.