Preheat the oven to 325°F and line a small loaf pan with parchment paper.
In a bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside. In another bowl, cream together the butter and sugar until light and fluffy. Mix in the egg and vanilla throughly and then the mashed avocado and lime juice. Gently fold in the flour mix, being careful not to over mix.
Spoon the batter (it is very thick) into the prepared pan and bake for 35-45 minutes or until an inserted wooden skewer is clean with a few crumbs clinging. Cool completely, slice and enjoy.