Mix all ingredients, except Nutella together in a big bowl with wooden spoon, until blended well. Spread in a parchment lined, non-stick sprayed 8” pan.
Spoon Nutella in 3 lines across batter. Swirl using a toothpick.
Bake at 350 for 25-30 minutes (toothpick should come out clean). Cool & cut into bars.