In a large mixing bowl, combine all ingredients except avocados. Mix well, cover and refrigerate at least 2 hours. When ready to serve, halve avocados lengthwise, removing and discarding pits. Using a tablespoon, remove peelings by carefully scooping out avocado flesh while keeping each half intact. Spoon an equal portion of crawfish salad into each avocado half. Serve on decorative multicolored lettuces as a salad or appetizer.