Preheat oven to 350 degrees F. Line an 8 inch square metal pan with parchment or foil and grease the bottom.
Combine flour, baking powder, soda and salt in a large mixing bow; set aside.
In medium bowl whisk together egg white, 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.
Hazelnut Frosting
Stir together the hazelnut spread, powdered sugar and cocoa powder, then stir in the maple syrup and milk and beat until smooth.