Preheat oven to 350º F. Melt a few tablespoons of butter and spread around a bundt pan, covering the whole surface. Cover the butter in granulated sugar.
Mix together coconut oil, butter and Truvia in your KitchenAid mixer. Add in eggs, bananas, Greek yogurt, and vanilla. Mix until combined.
In a separate bowl, stir together flour, baking soda, baking powder, salt and cinnamon. Slowly add to banana mixture until incorporated.
Pour into prepared bundt pan and place in oven for about 45-50 minutes, or until toothpick comes out clean. Let cool slightly before turning pan over onto a plate.
When ready to serve, mix together some powdered sugar and milk and drizzle over the bundt cake. Cut and serve. Enjoy!