Preheat oven to 350°F. Arrange bread cubes on tray and drizzle lightly with oil. Bake for 10 minutes, until just slightly golden brown. Remove from oven and set aside to cool.
Whisk together all ingredients for the dressing.
In a large bowl, combine tomatoes, toasted bread, red onion, cucumber, and basil. Pour in the dressing and stir to coat.
Allow salad to chill in the fridge for about 15-20 minutes so the bread can fully absorb the dressing and the juice from the tomatoes. Give the salad a toss once or twice during this time.