I finally decided to have a go at making this, and it was a lot easier that I thought.
I followed Rick Bayliss's advice and waited 5 days for my store bought avocados to ripen. Then I spooned them out. Added chopped tomato, onion, cilantro, and jalapeno pepper. A dash of lime juice and a bit of salt, then mix.
Josh & I (mainly me) finished this off in one sitting.