Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper.
In a large bowl, mash bananas until smooth.
Whisk in tahini and maple syrup until fully combined.
In another bowl, mix almond flour, cocoa powder, baking powder, and salt.
Add the dry ingredients to the wet mixture. Stir until just combined.
Fold in chocolate chips (and hazelnuts if using).
Pour batter into the prepared pan.
Drizzle extra tahini on top and swirl with a toothpick for a pattern.
Bake for 25–30 minutes for fudgy brownies, or up to 35 minutes for cakier brownies.
Let cool at least 20 minutes before slicing.