Toast the Pecans: Preheat the oven to 300ºF (149ºC) and place the chopped pecans on a lined baking sheet in a single layer. Bake for 6-8 minutes, shaking the pan once at the halfway point, until toasted and fragrant. Let the toasted pecans cool to room temperature (about 10 minutes) before adding them to the cake batter.
Roast the Bananas (Optional): This optional step caramelizes the bananas and adds more depth of flavor! Preheat the oven to 350ºF (177ºC). Rinse the unpeeled bananas and pat them dry. Place them onto a baking sheet and use the tines of a fork to poke a few holes in each banana. Bake for 12-15 minutes, until the peels are dark brown/black and shiny. Remove from the heat and allow to cool to the point where the bananas are easy to handle. Peel them into a medium bowl, collecting all the juices and banana, then mash with a fork. Set aside to cool completely to room temperature before continuing on with the recipe. You can speed this part up by placing the mashed banana in the refrigerator.
Preheat the oven to 350ºF (177ºC). Prepare three 8-inch round cake pans by spraying the sides with baking spray and lining the bottoms with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, allspice, and salt. Set aside.
In a separate large bowl, add the brown sugar, granulated sugar, vegetable oil, eggs, and vanilla. Whisk together, then whisk in the mashed banana and crushed pineapple. Switch to a silicone spatula and add half of the flour mixture, folding until just combined before folding in the rest of the flour mixture. Then, gently fold in the toasted pecans.
Pour the batter evenly between the prepared cake pans and bake for 25-29 minutes, until a toothpick inserted comes out clean or with a few moist crumbs. Cool for 5 minutes before removing the cakes from the pans. Transfer the cake layers to a wire rack to cool completely to room temperature.