In a large bowl, combine dry ingredients. In another bowl, mash the bananas. Add egg, oil and vanilla; mix well. Stir into the dry ingredients just until moistened. Stir in chocolate chips. Fill greased or paper-lined muffin cups half full.
Bake at 375° for 18-22 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes; remove from pan to a wire rack to cool completely.