Preheat the oven to 350°F. Line a 9x9 inch pan with foil, overlapping on all sides. Set aside.
In a large bowl, combine flour, ¾ cup rolled oats, brown sugar, baking powder and salt and mix to combine. Pour melted butter into dry mixture in a thin stream, mixing it into the dry ingredients until it has the look of wet sand.
Scoop out about half of the mixture and place it in the prepared baking pan. Press down with your fingers to pack it down into a sturdy base.
To the remaining mixture, add the rest of the oats and the hazelnuts, mixing to combine. Set aside.
Spread strawberry jam over the bottom layer in the pan, making sure to cover entirely.
Grab the remaining mixture by the handful, squishing it together to create a pebbly crumble and sprinkle it over the top of the jam. Cover completely.
Bake for about 40 minutes until the topping is lightly browned and the jam is bubbly. Remove from oven and allow to cool completely.
Place the chocolate hazelnut spread into a zip-top bag and snip one corner. Drizzle the crumble top with the spread. {You can also warm it up a bit to loosen it and just drizzle with a spoon for a more rustic look.}
Cut into bars and enjoy!