For the vinaigrette, combine the first 4 ingredients in a bowl. Add the vinegar and salt and let stand for 10 minutes. Add the olive oil and season with pepper; mix well.
For the salad, cut the larger tomatoes into bite-size pieces. Combine the tomatoes in a salad bowl and toss to mix. Chill until serving time.
Add the vinaigrette to the tomato mixture and toss to mix well. Spoon onto serving plates and top with cucumber and basil.