Grease a standard-size loaf pan and line it with a parchment paper sling.
In a large bowl, whisk together the mashed banana, pumpkin puree, vegetable oil, and eggs. Add the remaining ingredients except for the chocolate and stir well to combine and make a smooth batter. Fold in the chocolate chips if using. Transfer the batter to the prepared pan and smooth the top. Rest the batter for up to 20 minutes.
Preheat the oven to 350℉. When the batter has rested, place the loaf in the oven and bake for about 55-60 minutes, until the loaf has risen nicely and a tester inserted in the center comes out clean.
Cool the loaf in the pan set on a wire rack for 15 minutes, then turn it out onto the rack to cool completely to room temperature.
Notes
Oat flour substitute - Sorghum or teff flour are always great choices for an oat flour replacement, especially sorghum flour which performs similarly to oat flour. You can also try brown rice flour.
Almond flour substitute - If you can't eat almonds, try another nut flour that you can tolerate. Or, substitute ¼ cup of oat flour for the almond flour.
Adjust the sugar - If your banana is very ripe (ideal) and sweet, you can reduce the amount of added sugar if you wish.
Use unrefined sugar - Coconut sugar or pure maple syrup are lovely additions to pumpkin banana bread and have the added bonus of being refined sugar-free. Use them as a 1:1 replacement for the brown sugar.
Ripe bananas! As with most banana recipes, please use a ripe banana for the best natural sweetness! A nicely ripe banana will be bright yellow with some brown spots and streaks.
Rest the batter - Make sure to allow for about 20 minutes for the gluten free batter to rest and hydrate (this will make for a fluffier crumb) before baking the loaf. If you're short on time, let the batter rest for at least the time it takes for the oven to heat.