Preheat oven to 350 degrees F.  Line an 8 or 9 inch square pan with parchment paper.

Make the crust.  In a medium bowl, stir together almond and hazelnut flour, along with tapioca starch and coconut sugar.  Add the oil and stir until the dough comes together.  Press into the bottom of the pan.

Wipe out the bowl and make the almond paste.  Stir together the almond flour and butter, along with the tapioca, sugar, vanilla, and olive oil until a relatively creamy and spreadable paste forms.  You can use a food processor to get it super creamy but the almond butter and some stirring does the trick quite well.

Spread the paste over the crust.  Wipe the bowl out again and stir together the rhubarb and lemon juice and zest.  Pour over the paste and spread into an even layer.

Wipe the bowl out again and make the topping.  Stir together the almond flour, hazelnuts, coconut sugar and flour, and tapioca.  Add the oil and stir until clumps form.  Sprinkle over the rhubarb and bake 50-60 minutes until the rhubarb is knife tender.  Cool completely in the pan before cutting and serving.  Bars may be stored in an airtight container at room temperature for up to 3 days or frozen, wrapped in parchment and foil and placed in a zipper bag for up to 3 months.  Thaw at room temperature about an hour or in the microwave about 1 minute.