In a medium bowl, combine the tomatoes, onion, 1 tablespoon of the oil, vinegar, salt, and pepper. Toss well. Set aside at room temperature for 30 minutes.
Arrange the bread slices on a baking sheet. Brush the slices with the remaining 1 tablespoon oil. Broil for 1 to 2 minutes, or just until toasted on 1 side. Watch carefully, as the bread can burn quickly.
Divide the tomato mixture among the toasts and serve.