Preheat oven to 350°F. Lightly coat an 8x4-inch loaf pan with spray oil. (Alternatively, use three 5x3-inch mini loaf pans.)

In a bowl, whisk together both flours, flaxseed, 2 teaspoons of the cinnamon, baking soda and salt; set aside.

Using an electric mixer fitted with the paddle attachment, beat together butter and granulated sugar until creamy.

Add eggs, one at a time, beating well after each addition.

Beat in yogurt, bananas and vanilla.

Sprinkle in flour mixture and beat until just incorporated. Spoon batter into the prepared pan.

In a small bowl, stir together turbinado sugar and remaining 1 teaspoon cinnamon. Sprinkle over top of batter.

Bake until a knife inserted in center of loaf comes out clean, 55 to 60 minutes. (If using a glass loaf pan, decrease the baking time by 5 to 10 minutes. If using mini loaf pans, bake for about 40 minutes.)

Transfer the pan to a wire rack and let cool for about 5 minutes.

Remove bread from the pan and continue to cool on the wire rack. Serve immediately or wrap and store at room temperature for up to 3 days.