Preheat oven to 350 degrees F. Line an 8 inch square metal pan with foil and spray with flour-added cooking spray.
Combine flour, baking powder, soda and salt in a large mixing bow; set aside.In medium bowl whisk together egg whites, maple syrup, oil, milk and vanilla; add to flour mixture. Stir to combine. Stir in the cooled toasted nuts and the chocolate.
Spread in prepared pan.
Bake 25 to 30 minutes or until a toothpick inserted near center comes out clean. Cool on wire rack and then lift from pan.
Spread with Chocolate-Hazelnut Frosting or put the frosting in a freezer bag, snip off the bottom corner, and pipe stripes of it over the top.
