Preheat oven to 350F with rack on lower middle position. Grease two 9x5 loaf pans and set aside.
In bowl of a stand mixer, use paddle attachment to cream together the butter and sugar until light yellow and fluffy, 3-5 min. on medium speed. Beat in eggs one at a time until combined. Add orange zest, mashed avocado, and mix to combine.
In a separate bowl, stir in the flour, baking soda, baking powder, salt, ground cinnamon, and ground allspice until combined. Stir dry mixture into the butter mixture, followed by half of the buttermilk, mixing until just combined. Repeat with remaining flour mixture and remaining buttermilk, mixing just until incorporated (don't over-mix.) Use a rubber spatula to fold in the chocolate chips and pecans just until combined. Divide batter evenly between the two greased loaf pans.
Bake 60- minutes in preheated oven, until toothpick inserted into center of both loaves come out with tender crumbs attached. Cool fully on wire rack before carefully removing from pans.