Preheat oven at 350. Prepare a 9 "x 9" pan with cooking spray. To prepare bars, combine flour, baking powder, sugar, milk powder, and malted balls in a mixing bowl. In another mixing bowl, combine margarine, eggs, fat-free milk, and vanilla extract. Mix dry ingredients with wet ingredients just until moistened. Spread mixture into prepared pan. Bake for 30 minutes. Meanwhile, to prepare frosting, combine powdered sugar, cocoa powder, margarine, water, and remaining vanilla extract. Mix until combined or desired spreading consistency. When bars are cool spread frosting and sprinkle with remaining milk balls.