Preheat the oven to 350ºF. Grease and flour two 8x4 inch loaf pans and set aside.
In a medium bowl, whisk together butter, oil, sugars, and eggs until thoroughly incorporated. Whisk in the vanilla, yogurt, and bananas. Set aside.
In a large bowl, whisk together flours, salt, baking soda, and cinnamon. Stir in millet. Make a well in the center of the dry ingredients. Add the wet ingredients to the well and use a spatula to fold the batter together.
Divide the batter between the two prepared baking pans. Bake for 50-60 minutes or until a toothpick inserted in the center of a loaf comes out clean. Remove the pans from the oven and allow to cool for 15 minutes before inverting onto a wire rack to cool completely.