Preheat the oven to 180 C / Gas 4. Grease and flour two 23x13cm loaf tins. Sieve together the flour, bicarbonate of soda, baking powder, salt, cinnamon and allspice. Set aside.
In a medium bowl, cream together the sugar and butter until light and fluffy. Beat in the eggs one at a time, then mix in the mashed avocado. Stir in the dry ingredients alternately with the buttermilk until just mixed. Fold in the chopped pecans, raisins and orange zest. Divide the batter evenly between the two loaf tins.
Bake for 1 hour in the preheated oven or until a skewer inserted into the centre of the loaf comes out clean. Allow loaves to cool in pan for at least 20 minutes before removing.