Preheat the oven to 350 degrees. Lightly grease a 9x11 or 8x11 baking dish (or a large oval baking dish)and set aside.
In a large bowl, mix together the blueberries, coconut sugar, lemon zest, and arrowroot starch. Add the lemon juice, gently stirring to combine. Let sit for about 5 minutes.
In a small sauce pan, melt the plant based butter (if you’re not dairy-free/vegan, use grass fed butter).
In a medium bowl, mix together the gluten-free flour, coconut sugar, cinnamon, and salt. Fold in the vegan butter (or real grass fed butter), and stir to combine, using a fork or pastry knife if necessary.
Pour the blueberry mixture into the prepared dish. Spoon the crumble topping evenly across the top of the dish. Transfer to the oven and bake for 25-28 minutes, or until bubbly. If you bake for 25 minutes, topping should be softer and more chewy. If you bake a few minutes longer, you’ll have more of a crunchy topping. I prefer the crunchier sort of crumble, but bake it the way you like it.
Enjoy warm on its own or even with vanilla ice-cream (use your favorite dairy-free ice-cream to keep it vegan). Keep at room temperature. Best enjoyed within two days.