Preheat the oven to 180°C (gas mark 4). Grease a baking sheet.
In a large mixing bowl, cream the avocado using an electric mixer. Add the brown sugar and mix well. Add the eggs and vanilla and continue beating until well-mixed.
Into a large bowl, sift the flour, baking soda, cinnamon, nutmeg, and salt. Add to the avocado mixture. Beat slowly, gradually increasing the speed to mix well. Mix in by hand the oats and walnuts, and raisins, if desired. Drop the mixture by the tablespoonful onto the greased baking sheet.
Bake for 10 to 12 minutes or until cooked. Remove from the oven, cool, and serve.