Preheat the oven to 400°F and grease an 8x8-inch or similar baking dish.

In a large bowl, combine the blackberries, sugar, cornstarch, lemon juice and zest, and vanilla and toss to coat.

Make the topping: In a medium bowl, combine the oats, almond flour, brown sugar, walnuts, cinnamon, and salt. Using your hands, work in the firm coconut oil until the mixture is crumbly.

Scoop the blackberry filling into the prepared baking dish. Evenly sprinkle on the topping and bake for 25 to 35 minutes, or until the fruit is bubbling and the topping is golden brown.

Remove from the oven and let cool for 5 minutes. Serve with vanilla ice cream.