Preheat oven to 350°F. Line a baking sheet with parchment paper.
Toss cubed challah on the prepared sheet with 2 tablespoons evoo and toast for 5 to 10 minutes until lightly golden brown.
Add vinegar to a large bowl. Add tomatoes and garlic, toss, and marinate for 5 minutes.
Add onion and cucumber to bowl and mix to combine with tomato-vinegar mixture. Add ¼ cup of evoo and toss. Add challah, torn basil leaves, salt and pepper and toss together. Serve immediately.