Preheat oven to 350°F. Spray a 9 x 5″ loaf pan with non-stick baking spray and line with parchment paper, allowing it to extend over the sides for easy removal. Melt the butter in a small pot (or microwave) and let cool for 10 minutes. Mash the ripe bananas with a fork until smooth. In a medium bowl, whisk together melted butter and brown sugar for 30 seconds. Add eggs and vanilla, whisking to combine. Stir in mashed bananas. In a separate bowl, whisk together flour, baking soda, baking powder, salt, and cinnamon. Fold half of the dry ingredients into the banana mixture, then add Greek yogurt and mix until mostly incorporated. Add remaining dry ingredients and mix until just combined. Transfer batter to the prepared loaf pan. Optionally, place a halved banana on top and sprinkle with turbinado sugar. Bake for 55 to 60 minutes until golden brown and a toothpick comes out clean. Cool in the pan for 10-15 minutes before removing and cooling completely on a wire rack.