put the baked (and cooled) oat cookie, brown sugar, salt, and melted butter into a food processor and pulse until the cookie is broken down and the butter has made the mixture moist (adding another 1-1 1/2 tablespoons butter if needed). alternatively, you can crumble and mix this with your hands, but the food processor works better.
using your fingers and the palms of your hands, press the oat cookie crust firmly into a pie plate, making sure the bottom and sides of the pie plate are evenly covered.
tumble the berries onto the oat cookie crust and top with the crack pie filling. bake the pie in the preheated oven for 15 minutes.