In a blender or food processor, combine half the mango with the water, ginger ale, vinegar, oil and sugar. Purée until smooth. Season with salt and pepper. Transfer the soup to a non-reactive bowl. Cover and refrigerate until cold, about 4 hours. In another non-reactive bowl, combine the remaining 4 cups mango, cucumber, red onion and 1/2 cup cilantro. Cover and refrigerate until cold. To serve, divide the cucumber mixture among chilled soup bowls that are each sitting in a bowl of crushed ice. Ladle the soup over the cucumber mixture and sprinkle with the remaining 1/4 cup cilantro. Serve immediately. Serves 4 to 6.