1Heat oven to 375°F. Grease bottoms only of 12 regular-size muffin cups with shortening or spray, or line with paper baking cups.
2In medium bowl, beat 2/3 cup sugar, the oil and eggs with wire whisk. Stir in bananas and vanilla. Stir in remaining muffin ingredients just until moistened. Divide batter evenly among muffin cups.
3Bake 17 to 21 minutes or until toothpick inserted in center comes out clean. Immediately remove from pan to cooling rack.
4In small bowl, mix 1/4 cup sugar and 1/2 teaspoon cinnamon. Dip muffin tops into melted butter, then into cinnamon-sugar. Serve warm.