Preheat oven to 350 degrees F. Line a loaf pan with parchment paper by using a little cooking spray or coconut oil to get the paper to fit snugly.
Combine tahini and chai spices until smooth and set aside. Toast walnuts in a pan, then give them a rough chop. Whisk together flour, baking powder, baking soda, and salt in a large mixing bowl and set aside.
Add the bananas, eggs, chai tahini mixture, brown sugar, coconut oil, and vanilla to a blender and blend on low speed until combined. You can also do this in a mixing bowl—just mash the bananas with a fork before adding the other ingredients.
Pour contents into the bowl with the flour mixture and fold with a spatula to combine. Gently stir in walnuts and 1-2 tbsp black sesame seeds until just combined. Don’t over mix.
Pour batter into loaf pan and sprinkle a bunch of black sesame seeds over the top. Slice banana in half lengthwise and place on top of batter with the cut side face up.
Bake for 30-40 minutes until a small knife or toothpick comes out mostly clean. I like to test in at least 3 places. Remove from the pan immediately and cool completely on a wire rack before storing in plastic wrap, foil, or an airtight container at room temperature.