In a large bowl, beat butter and sugar until crumbly, about 2 minutes. Add eggs, one at a time, beating well after each addition. Beat in the bananas, yogurt and vanilla.

Combine the flours, baking soda, salt and cinnamon. Gradually beat into the butter mixture. Stir in peanut butter chips.

Remove 1 cup batter to a small bowl, stir in chocolate until well blended. Poor half of the remaining plain batter into a 9 by 5 inch loaf coated with cooking spray. Top with half of the chocolate batter. Repeat layers. Cut through batter with a knife to swirl.

Bake at 350 for 40 to 50 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes before removing from pan to a wire rack.