Place the watermelon, tomatoes, cucumber, red bell pepper, red onion, garlic, mint, olive oil, sherry vinegar, lime juice, salt, black pepper, cumin, and soaked bread in a blender. Blend until mostly smooth while leaving a little texture.

Taste the soup and adjust seasoning by adding more salt, pepper, or sherry vinegar if needed.

Transfer the blended soup to a bowl, cover, and refrigerate for at least 4 hours. Serve cold with a garnish of fresh mint if desired.