Queen avocado, or palta reina, as this popular dish is called in South America, is royally rich but perfectly simple. It's a great summer lunch and a real crowd-pleaser. I like to make my chicken salad with plain yogurt (not Greek yogurt, which is too thick) instead of mayonnaise to make it lighter.
Bring a pot of salted water to boil (just enough to cover the chicken), and add in the chicken breasts and simmer for about 25 minutes. Remove and allow to cool, and then shred the poached chicken and put into a bowl. Mix in the celery, yogurt, salt, pepper, and mustard. Refrigerate for an hour or so until cool.
Halve avocados lengthwise and remove the peel. Spoon the chicken salad in the center of the avocado and garnish with a dash of paprika. Serve atop greens.