Preheat oven to 375°F (190°C) and grease an 8x8 inch baking dish.
In a large bowl, toss blackberries with the first portion of maple syrup, lemon juice, and lemon zest.
Transfer the blackberry mixture to the prepared baking dish.
In a separate bowl, combine oats, almond flour, chopped walnuts, cinnamon, and sea salt.
Stir in the melted coconut oil and the second portion of maple syrup until the mixture is crumbly and well-coated.
Sprinkle the crumble topping evenly over the blackberries.
Bake for 30 to 35 minutes, or until the fruit is bubbling and the topping is golden brown.
Allow to cool for 10 minutes before serving.