My good friend and mentor, David Scribner, taught me how to make this soup. He was messing around with new dishes once, trying to impress a girl, and came across the combination of dill and avocado. I have made this soup ever since and love the versatility of the garnish, which can range from sliced crisp vegetables to seafood. With its beautiful green hue, this cold soup is equally well suited to serve at a formal dinner or a picnic.
Scrape the avocado flesh from the skins into a blender. Reserve a few sprigs of the dill for garnish and add the rest, along with the half-and-half and lime juice, to the blender. Season generously with salt and blend on high speed until you have a very fine purée. If the soup is too thick, add a few extra tablespoons of half-and-half or water. Transfer to a bowl and cover with plastic wrap, pressing the wrap against the surface of the soup to keep the soup from discoloring. Chill in the refrigerator for at least 1 hour (you can refrigerate it up to a day, but there will be some discoloration).
To serve, divide the shredded trout among 4 bowls. Sprinkle with the olive oil and add the remaining sprigs of dill. Season with a few cracks of pepper. Ladle the chilled soup into the bowls.