Beat margarine at medium speed of an electric mixer until creamy; gradually add 1 1/3 cups sugar, beating well. Add egg whites and next 4 ingredients; beat well.
Combine flour, baking powder, salt, and 2/3 cup cocoa; add to margarine mixture, mixing well. Pour batter into a 13- x 9- x 2-inch pan coated with cooking spray. Bake at 350° for 20 to 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack.
Combine powdered sugar and 1/4 cup cocoa; stir well. Add water, 1 tablespoon at a time, stirring until smooth. Pour over brownies, and spread evenly. Sprinkle with crushed peppermint. Let stand 10 minutes before cutting into bars.