Preheat the oven to 350 degrees F.
Add the rolled oats, oat flour, almond flour, brown sugar, salt, and two tablespoons cold butter to a bowl. Use a pastry cutter and mix the butter into the flour mixture to form a crumbly mixture.
Add the sliced almonds and mix.
Add the berries, vanilla, lemon juice, and corn starch to a bowl. mix.
Transfer to a oven safe 5.5X5.5-in or 6x6-in dish.
Add the oats crumble on top. Add the remaining butter on top. Bake for 27-28 minutes, or until the mixture is bubbly and golden on top.
Remove from the oven, cool.
Serve with whipped cream or ice cream.