Preheat the oven to 350°F and line a 9 x 9 square pan with parchment paper or butter and flour the pan. Set aside.
In a large mixing bowl, combine the mashed bananas, melted butter, and sugar. Add the eggs and vanilla extract and mix well. Add the greek yogurt.
In a separate bowl stir together the the dry ingredients. Add the dry ingredients and mix until just combined. Pour half of the batter into your prepared pan and set aside while you make the cinnamon sugar swirl and the crumb topping.
In a small bowl combine the cinnamon and brown sugar and a pinch of salt. Stir together to mix well. In a separate bowl, stir together the flour, sugar and salt for the crumb topping. Use a fork or a pastry cutter to cut the butter into the dry ingredients until the mixture starts to clump together and looks like wet sand.
Spread the cinnamon sugar swirl over the first layer of banana bread. Pour the remaining batter over the cinnamon sugar. Top with the crumb topping, spreading into an even layer.
Bake for 40 minutes or until a knife inserted into the middle comes out mostly clean. Allow to cool before serving. If desired, dust with powdered sugar.