In a large bowl, whisk together the flour blend, teff flour, cocoa powder, cinnamon, baking soda and salt.
In a medium bowl, whisk together the sugar, eggs, butter and vanilla until well blended. Whisk in the bananas and yogurt until blended.
Add the egg mixture to the flour mixture and stir until well blended. Gently fold in the chocolate.
Using a greased 12-cup muffin pan, divide the batter equally among the prepared muffin cups.
Bake in a preheated oven for 20 to 25 minutes or until a toothpick inserted in the center comes out clean. Let the muffins cool in the pan on a wire rack for 5 minutes, then transfer them to the rack to cool.