Preheat oven to 350ºF. Measure the flour, baking powder, baking soda and nutmeg into a medium bowl.
In a large bowl, start by mashing the bananas. Leave them a bit chunky. Then add in the butter or oil, miso paste, vanilla, and the sugars, mix, then add in the eggs and buttermilk and mix some more. You can use a mixer for this if you like, but doing it by hand is easy and works out just fine.
Mix until everything is uniform and smooth—it won’t take long. Then add in the dry ingredients a bit at a time. You want everything to be just blended together but not overmixed. The batter will be rather thick (but not anywhere as thick as the blueberry bundt cake we made a couple of weeks ago).
Lightly butter and flour the loaf pan. Scrape the batter into the pan and level it gently with your spatula. Artfully scatter the pumpkin and sunflower seeds on top—you may want to gently press them in a little bit.
Set in the middle of the oven. After 30 minutes, rotate the pan 180 degress. Bake for a total of approximately 60 minutes. Keep an eye on the bread and test at about 50 minutes—the tester inserted near the center should come out clean. If the top is browning but the center is not baked yet, put a piece of foil on top.
When it is done, let it cool in the pan on a rack for an hour, then turn it out onto the rack to finish cooling.