Make the kabocha squash puree. Preheat the oven 400°F/205°C. Cut a kabocha squash in half and lightly brush with a neutral oil. Place on a parchment paper-lined baking sheet, flesh side down, and bake for 45 minutes until very tender. Once cool enough to handle, scoop the flesh into a food processor, discarding the skin, and blend until completely pureed. Position a fine mesh sieve over a bowl and pour the squash into the sieve. This removes the excess liquid and ensures your puree isn’t too watery. Then measure out 240 grams, or about 1 cup, of the puree. You can also make the kabocha squash puree in advance.
Reduce the oven temperature 350ºF and grease a 9×5-inch loaf pan well or line it with parchment paper to prevent sticking. Position a rack in the middle of your oven.
Make the Cinnamon Walnut Streusel (if using): Mix all of the ingredients except the coconut oil in a small bowl. Then add in the solid coconut oil and mix together with your fingers until it resemble coarse crumbs.
In a medium bowl, sift together the gluten-free flour, almond flour, baking powder, baking soda, salt, cinnamon, nutmeg, ginger, and cloves (if using). Stir well to incorporate.
In a large bowl, mash the bananas. It’s fine if there are some lumps left. Then add the kabocha squash puree, almond milk, avocado oil, coconut sugar, and vanilla. Whisk until well combined.
Gently add the dry ingredients into the wet, and mix until the batter is just combined and no streaks of dry ingredients remain. About 15-20 light strokes by hand should do the job. Overmixing can in a tougher or denser texture and irregular “tunnels” or air holes in the loaf.
Pour the batter into the prepared loaf pan. Sprinkle the Cinnamon Walnut Streusel (if using) evenly on top of the banana bread batter.
Bake the banana bread for 35 minutes. Then loosely tent the loaf with a piece of aluminum foil to ensure even cooking and prevent premature browning. Cook for another 20-30 more minutes (for a total of 55 to 65 minutes), or until a toothpick comes out of the center and top clean. I recommend checking at 50 minutes just to be sure, since all ovens are a bit different. If the bread is too moist when you check it, bake for another 5 minutes.1. NOTE: If your loaf pan is an 8×4-inch pan (instead of the standard 9×5-inch pan), your loaf will be even thicker due to the smaller pan size, so you might need to bake the loaf a bit longer, even up to 70 minutes.
Transfer the banana bread to a wire rack and cool before slicing. To store, wrap the loaf in plastic wrap and leave on the counter for 1-2 days, or in the fridge for up to 1 week.