Roughly chop the melon and add to the bowl of a food processor, reserving some for garnish. Chop the cucumber and halve the grapes and add to the food processor. Top with the spinach, basil, scallions and serrano. Splash in the olive oil, champagne vinegar, lime juice and honey. Process until the ingredients are combined, about 1 minute. Add half the avocado and process again until the avocado has been completely incorporated, about 30 seconds. Season to taste with salt and pepper and thin with ice water if necessary to reach desired consistency.
Transfer to a bowl, cover and refrigerate for at least 1 hour.
To serve: Ladle the soup into bowls and top with the diced honeydew, sliced avocado, and cilantro leaves. Serve with wedges of lime on the side.