Preheat oven to 350°F (180°C). Line a standard loaf pan with parchment paper, leaving overhang on both sides.
In a large mixing bowl, whisk together the almond flour, baking powder, baking soda, salt, and cinnamon if using.
In a separate bowl, mash the bananas until mostly smooth.
Add the eggs, Greek yogurt, melted butter, coconut sugar (or allulose), and vanilla extract. Whisk until fully combined.
Pour the wet ingredients into the dry ingredients and mix until no dry almond flour remains.
Transfer the batter to the prepared loaf pan and smooth the top. Add banana slices if desired.
Bake uncovered for 20 minutes.
Loosely cover the loaf with foil and continue baking for approximately 40 more minutes, or until a skewer inserted into the center comes out clean.
Allow the loaf to cool in the pan for 15 minutes.
Transfer to a wire rack and cool completely before slicing.