Heat grill to medium. Brush bread slices on both sides with 2 tablespoons oil. Grill until lightly charred on both sides, 3 to 4 minutes. Let cool slightly, then cut into large cubes.
In a large bowl, toss bread cubes with tomatoes, cucumber, and basil. Drizzle with vinegar and remaining 1/4 cup oil, and season with salt and pepper. Toss to combine, and serve.
Yum! This is GOOD!