Start by preheating your oven to 375 degrees Fahrenheit. Lightly grease an 8-inch square baking dish or a similar sized pie plate with a little bit of butter or oil to prevent sticking. Set the dish aside while you prepare the fruit and the topping.
In a medium mixing bowl, combine the fresh or frozen cranberries, granulated sugar, orange zest, orange juice, alcohol-free vanilla, and cornstarch. Stir everything together until the berries are evenly coated and the sugar begins to look slightly damp. Pour this mixture into your prepared baking dish and spread it out into an even layer.
In another bowl, whisk together the rolled oats, all-purpose flour, brown sugar, cinnamon, and salt. Add the cold, cubed butter to the dry ingredients. Use a pastry cutter or your fingertips to work the butter into the mixture until it looks like coarse crumbs with some pea-sized pieces remaining.
Sprinkle the oat topping evenly over the cranberry mixture in the baking dish. Place the dish in the center of the oven and bake for 35 to 40 minutes. You will know it is done when the topping is golden brown and the cranberry juices are bubbling up around the edges. Remove from the oven and let it cool for at least 10 minutes before serving to allow the filling to thicken.
