Choose heavy, undamaged avocados. One that yields slightly to pressure is best for slicing and dicing; if pressure leaves a small indentation, the avocado is best mashed. Avoid very soft avocados, as they will be overripe and unusable.
It's best to prepare this the day or night before you want to serve it, but not more than that. This also makes it the perfect dessert for summer entertaining: It's cool, light, refreshing, and impressive.
Watercress gives a simple salad zest -- and an abundance of vitamin C.
Segments of pink grapefruit supply additional vitamin C and also the cancer-fighting
antioxidant lycopene. Chopped walnuts offer heart-healthy alpha-linolenic acid.