Preheat the oven to 350°F. Grease a metal loaf pan with nonstick spray, butter or shortening. Set aside.
Add the butter to a microwave safe bowl and microwave on high until melted. Add the bananas the same bowl and mix until combined. Add in the vanilla and eggs and stir until the egg yolk is fully combined.
In a seperate large bowl, whisk together the dry ingredients (flour, sugar, baking soda, salt) and stir to combine.
Mix the dry ingredients into the wet ingredients and stir until just combined. Be sure to not overmix. Divide the batter into two equal bowls, add the matcha powder to one and stir until the color is uniform.
Alternate scoops of each batter in the loaf pan. Swirl the batters together to get a beautiful marbling. Place the halved banana on the top of the loaf cut side up.
Bake the loaf for 55-65 minutes, or until a toothpick inserted into the center comes out clean. I like to add a bit of cooking spray for the last 10 minutes of baking to crisp up the edges and crust - but this is optional.
For best texture, allow to cool on a wire rack until cooled completely. Store covered for up to 3 days on the counter or 6 days in the fridge.
Matcha Powder - for drinking, I always use ceremonial matcha but any food grade matcha will work. Price doesn't always equal quality, but you do want to enjoy the taste.