Preheat oven to 350°F (180°C). Line 12-cup muffin pan with cupcake liners; set aside.
Lightly beat Hellmann's® 1/2 The Fat mayonnaise-type dressing, granulated sugar, eggs and vanilla in small bowl with wire whisk or fork; set aside.
Sift flour, cocoa powder and baking powder into large bowl. Add egg mixture and beat with wire whisk or fork just until combined. Evenly pour into prepared pan.
Bake 15 minutes or until toothpick inserted in centers comes out clean. Cool 10 minutes on wire racks; remove from pans and cool completely.
Meanwhile, beat confectioners sugar, margarine and peanut butter in medium bowl with electric mixer until smooth. Frost cupcakes with peanut butter frosting. Decorate, if desired, with chocolate sprinkles or other cake decorations.