HEAT oven to 375°F.
COMBINE first 5 ingredients in large bowl. Whisk peanut butter and milk in medium bowl until blended; stir in bananas, egg, oil and vanilla. Add to flour mixture; stir just until moistened.
SPOON into 12 muffin pan cups sprayed with cooking spray.
BAKE 18 to 20 min. or until toothpick inserted in centers comes out clean. Cool slightly.