The easiest way to prevent an avocado from browning is to eat the whole thing in one sitting, but if you just want a couple of slices, a thin coating of oil can prevent the rest from oxidizing.
Photo by cyclonebill.
Serena Bass at Epicurious uses a thin coating of Pam to keep her avocados looking fresh; a fine mist kept one half bright and green for three days just sitting on a counter. You could use trusty ol' Pam, but I don't see why a mist of olive oil or even avocado oil (meta) wouldn't accomplish the same thing. No matter what oil you spray onto the delightfully fatty fruit, it will create an oxygen barrier, keeping your avo perfectly pretty until your ready to polish it off. Just wipe of the excess oil and enjoy!
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