Place the tomatoes, cucumber, red bell pepper, red onion, and garlic cloves in a blender. Blend until the mixture reaches a smooth consistency.
Add the olive oil, red wine vinegar, salt, and black pepper to the blender. Blend again until fully combined.
Transfer the soup to a container and refrigerate for at least two hours to chill thoroughly.
While the soup chills, heat a grill or grill pan over medium heat. Grill the bread cubes for two to three minutes, turning once, until they show light char marks and feel crisp.
Ladle the chilled soup into bowls. Top each serving with grilled bread cubes and a few fresh basil leaves.