Heat oven to 375°. Place cucumber in colander; sprinkle with 1/4 teaspoon salt. Place weight (such as a large zip-lock bag filled with water) over cucumbers; drain to release most of moisture, about 30 minutes. Rinse and pat dry. Place bread pieces on baking sheet; bake until crisp but not browned, 5 to 7 minutes. Transfer to large bowl; add cucumber, tomatoes, scallions and herbs, and toss well. In small bowl, combine oil, lemon juice, and salt and pepper to taste. Add to large bowl, toss again and serve immediately. Serves 6.