Stir together flour, granulated sugar, baking powder, soda, salt and poppy seeds. Set aside.
In large mixing bowl, combine KELLOGG'S ALL-BRAN cereal, milk, egg whites, oil, yogurt and lemon peel. Let stand about 5 minutes or until cereal softens. Add flour mixture, stirring only until combined. Spread evenly in 8 x 8 x 2-inch pan coated with cooking spray.
Bake at 350° F about 25 minutes or until wooden pick inserted in center comes out clean. Cool and dust with powdered sugar before serving.