Preheat oven to 350° Fahrenheit. Adjust oven racks as needed so bread will sit in center of oven. Line loaf pan with parchment paper, folding excess paper over edges of pan to create handles. Set pan aside.
Peel 3 medium over-ripe bananas and place bananas in large bowl. Using silicone spatula, mash bananas into very fine, almost liquid consistency.
Crack 3 large eggs directly into small mixing bowl. Whisk vigorously until eggs are beaten and fully combined. Pour beaten eggs into large bowl with mashed banana.
Add ¼ cup refined coconut oil, 1 cup coconut sugar, 1 cup superfine blanched almond flour, ¾ cup coconut flour, 1 teaspoon fresh baking soda, ½ teaspoon salt, 1 teaspoon pure vanilla extract, and ½ cup finely chopped walnuts to mixing bowl. Stir gently until ingredients are combined, but do not over-mix. Mixture does not need to be completely smooth.
Transfer mixture into prepared loaf pan. Spread batter out evenly across pan and into each corner.
Optional: Add layer of coconut sugar to shallow bowl. Halve 1 medium banana and place in bowl of coconut sugar. Press each banana half into coconut sugar and turn to coat all sides of banana well. Place sugared banana halves on top of bread batter and press halves gently into batter.
Place loaf pan in preheated oven. Bake banana bread 45 minutes, then begin checking doneness with toothpick or butter knife. Insert toothpick into center of banana bread, then immediately remove toothpick from bread.
If toothpick is covered in wet batter or many crumbs, return loaf pan to oven. Continue baking banana bread as needed, checking doneness every 5 minutes, until toothpick comes out mostly clean, with very few crumbs.
When bread is fully baked, carefully remove loaf pan from oven. Set pan aside and allow bread to cool 5 minutes, then use excess parchment paper to gently lift bread out of pan.
Slice loaf into desired number of slices and serve warm.