Place the oats, milk, sweetener, and cinnamon in a medium to large bowl and stir. Cover with plastic wrap and refrigerate over night. Do not add the egg or baking powder.The next morning, preheat the oven to 350 degrees and grease an 8x8" square baking dish. Set aside.Whisk the beaten egg and baking powder into the oatmeal mixture until there are no lumps. Stir in the berries. Pour the mixture into the prepared baking dish and bake for 20 minutes or until the majority of the liquid is absorbed.While the oatmeal bakes, prepare the crumble. Stir the oats, flour, and sugar, and pinch of salt together in a medium bowl. Stir in the melted coconut oil and let stand until the oatmeal has absorbed most of the liquid. Top the oatmeal evenly with the crumble and continue to bake for 20-30 minutes, or until puffed, bubbly, and golden brown.If the oatmeal is puffed and bubbly but the crumble hasn't browned, place it on the middle rack under the broiler for a few minutes until golden.Remove from heat and let stand 10-15 minutes. Serve and enjoy!