Line an 8x8 baking dish with parchment paper and preheat the oven to 350°F.
Place the oats in a food processor and pulse until it forms a coarse flour.
Place the oats in a large bowl and add the flour, baking soda, salt, sucanat, and cinnamon.
Cut in the butter and incorporate into the dry ingredients with a pastry blender or in a food processor.
Take ⅔ of the mixture and press it into the bottom of the baking dish until it evenly covers the bottom.
Using an offset spatula, spread the cooled rhubarb filling over the bottom crust.
Take the rest of the oat crumble and sprinkle it on top.
Bake for 20-30 minutes, until the top crust becomes golden brown.
Let cool completely before slicing. Store in the refrigerator, but bring to room temperature before serving for best flavor. Enjoy!