Preheat oven to 350 degrees Fahrenheit.
Combine the frozen berries to the baking dish or cast iron. If using fresh berries, be sure to give them a good wash or soak them in water with a little vinegar.
Wash and dry the lemon then zest it using a microplane and add it to the berries. Cut the lemon in half and juice it. Add the juice to the berries.
Add the maple syrup and arrow root and stir until everything is fully incorporated.In a separate bowl, make the crumble topping by adding the almond flour, oat flour, maple syrup sugar, salt, mix the ingredients.
Chop the butter into pieces and add them to the dry ingredients, work the butter until it turns into a crumble consistency. Add the crumble to the top of the berries and place in the oven.
I recommend putting a scoop of vanilla ice cream on top. The cold ice cream in contrast to the hot dessert will send this dessert to a new level!