Preheat oven to 375°. In a large bowl, whisk flour, sugar, baking soda, cinnamon and salt. In another bowl, whisk egg, bananas, melted butter and vanilla until blended. Add to flour mixture; stir just until moistened. Fold in chocolate chips., Fill greased or paper-lined muffin cups three-fourths full. Bake 17-20 minutes or until a toothpick inserted in center comes out clean. Cool 5 minutes before removing from pan to a wire rack. Serve warm.