Preheat the oven to 350°F. Add the berries, sugar, gluten-free flour, salt, lemon juice and vanilla to a 9x9-inch or 8x11-inch baking pan. Mix to evenly combine. Bake for 10 minutes while you prepare the topping.
Pour the Walker’s gluten-free shortbread cookies into a large zipper-topped bag. Crush into small pieces and crumbs. In a medium bowl, combine the crushed cookies, gluten-free oats, almond flour, brown sugar, cinnamon and salt.
Add the cold cubed butter and toss it in the mixture until each piece is coated. Squish each cube of butter between your fingers to form small, thin sheets of butter. This will take some time, so keep working until the butter is no longer visible and the crisp mixture holds together when squeezed in your hand.
Remove the berries from the oven. Sprinkle the topping evenly over the berries.
Bake for 35-40 minutes, until the topping is golden brown and the berries are bubbling around the edges. Remove from the oven and let cool for 10 minutes before serving.