1. Prepare grill to medium-high heat.
2. Place bread slices on grill rack; grill 1 minute on each side or until golden brown with grill marks. Remove from grill; tear bread into 1-inch pieces.
3. Combine tomatoes, onion, bell peppers, basil, and cucumber in a large bowl. Add bread; toss gently.
4. Combine vinegar, black pepper, salt, and garlic in a small bowl, stirring with a whisk. Gradually add oil, stirring constantly with a whisk. Drizzle dressing over salad; toss gently to coat. Cover and chill 20 minutes before serving.