Whisk together both flours, baking soda, and salt in a small bowl. Combine sugar and oil in a separate bowl, and beat at medium speed with electric mixer until smooth. Add egg, and beat until light in color. Add flour mixture alternately with banana, blending well after each addition. Stir in vanilla and nuts, if using.
Scoop batter evenly into muffin cups coated with cooking spray. Bake 18-20 minutes, or until toothpick comes out clean. Cool completely on wire racks.
If desired, spread desired amount of peanut butter on muffins for serving.
Recipe by The eMeals Blog at http://blog.emeals.com/breakfast-meal-plan-simple-to-go-recipe-for-banana-muffins/