In a large bowl, beat eggs, sugar, oil, banana, yogurt, and vanilla to blend. In a smaller bowl, stir together whole-wheat and all-purpose flours, cocoa, cinnamon, salt, baking soda, and baking powder. Gently stir flour mixture and chocolate chips into egg mixture just until incorporated. Spoon batter evenly into 18 paper-lined muffin cups (3/4-cup capacity; fill them all the way to the top).
Bake muffins in a 350 regular or convection oven until a wooden skewer inserted into the center comes out with moist crumbs attached, about 25 minutes. Cool 10 minutes and remove from pans.
