Prep the pan. Heat the oven to 350°F with a rack in the center. Grease a 9 × 5-inch metal loaf pan and line it with parchment, leaving an overhang on the long sides.

Make the pecan crumbs. In a bowl, mix the flour, brown sugar, cinnamon, and salt with a fork. Stir in the melted butter until clumps form, then stir in the pecans. Set aside while you make the batter so the crumbs can firm up.

Brown the butter. Melt the butter for the loaf in a small saucepan over medium heat. Cook, stirring frequently and scraping the bottom, until the milk solids turn golden brown and the butter smells nutty, about 5–8 minutes. Immediately pour into a large heatproof bowl, scraping in all the browned bits. Let cool until warm, about 10 minutes.

Mix the batter. Whisk the brown sugar into the browned butter, then whisk in the mashed banana, pumpkin, eggs, and vanilla. In a separate bowl, whisk together the flour, baking powder, baking soda, cinnamon, pumpkin pie spice, and salt. Fold the dry ingredients into the wet ingredients. When just a few streaks of flour remain, add the chocolate and fold just until combined.

Top and bake. Scrape the batter into the pan and smooth the surface. Break up the topping with your fingers and scatter it over the batter in a mix of big and small clumps. Leave the crumbs loose, without pressing them into the batter. Bake for 65–80 minutes, checking at 60 minutes. If the topping is browning before the center is set, loosely tent the loaf with foil. It’s done when a skewer inserted in the center comes out with a few moist crumbs and no wet batter. If you hit melted chocolate, check a second spot.

Cool before slicing. Let the loaf cool in the pan for 20 minutes, then lift it onto a rack using the parchment. Cool completely so the center has time to set.