Preheat the oven to 325 degrees F. Spray a 9-by-5-inch glass loaf pan with cooking spray.
Whisk the flour, baking powder, baking soda and salt in a medium bowl. Add the granulated sugar, eggs and 2/3 cup tahini to the bowl of an electric mixer fitted with the paddle attachment and beat on medium speed until creamy, 3 to 4 minutes. Reduce the speed to low and add the bananas, oil, vanilla and cinnamon. Add the flour in 3 batches, making sure it is well combined after each addition.
Pour the batter into the prepared pan. Mix the black and white sesame seeds in a small bowl and sprinkle on top. Bake until deep golden brown and a skewer inserted into the center comes out clean or mostly clean with some moist crumbs clinging to it, about 1 hour and 20 minutes. Let cool in the pan for 15 minutes, then remove to a wire rack to cool completely, about 1 hour.
Stir together the confectioners' sugar, 4 teaspoons warm water and the remaining 2 tablespoons tahini in a small bowl until smooth. Drizzle the top of the bread with the glaze.
When measuring flour, we spoon it into a dry measuring cup and level off excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)
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