Recipe by gourmetkoshercooking.com 
¾ cup chopped pecans
½ cup flour
½ teaspoon baking powder
2/3 cup packed light brown sugar
¼ teaspoon salt
½ cup (1 stick) unsalted butter, melted
1 teaspoon vanilla extract
1 ½ cups old-fashioned rolled oats
¾ cup Nutella
Preheat oven to 375 degrees. Line an 8-inch squared baking pan with heavy-duty aluminum foil with at least 1 inch overhanging the top of the pan and sides.
In a food processor, grind the pecans coarsely. Add flour, baking powder, brown sugar and salt and pulse once or twice to combine. Add melted butter and vanilla and pulse until all ingredients are moistened. Add oats and pulse once or twice to combine.
Sprinkle half of the mixture across the bottom of baking pan and press it with your fingertips into an even layer. Place the other half of the mixture in the freezer for 5 minutes.
Spread the Nutella in an even layer on top of the crust. Scatter remaining crumb mixture over the Nutella, squeezing it into crumbs across the top. Bake until top is golden, 25 – 30 minutes.
Cut into 16 squares.