01 - Preheat the oven to 350°F.
02 - In a large mixing bowl, combine the berries, granulated sugar, cornstarch, vanilla extract, and lemon juice. Toss gently until evenly coated and transfer to an 8-inch baking dish.
03 - In a separate bowl, mix the oats, flour, brown sugar, sliced almonds, cinnamon, and salt. Add the cold butter and rub it into the dry ingredients with your fingertips until the mixture resembles coarse crumbs.
04 - Evenly scatter the oat crumble topping over the berry filling, covering completely.
05 - Bake for 35 minutes, or until the topping is golden brown and the berry mixture is bubbling around the edges.
06 - Allow to cool for 10 minutes before serving. Serve warm with vanilla ice cream or custard if desired.