Preheat oven to 375 degrees and line muffin pan with paper baking cups.
In medium bowl, whisk together 2/3 cup sugar, oil and eggs until combined.
Add mashed bananas and vanilla and stir together.
Add in remaining muffin ingredients and stir until just combined. Be careful not to overmix the batter.
Divide the batter among the baking cups.
Bake 18 minutes or until wooden pick inserted in center comes out clean.
Remove muffins from pan and allow to cool on wire rack.
For topping: Stir 1/4 cup sugar and 1/2 teaspoon cinnamon togethr in small bowl.
With a pastry brush, brush the muffins tops with the melted butter. Using a tablespoon, sprinkle the cinnamon-sugar mixture over the tops of the muffins.
Recipe adapted from Betty Crocker