In a medium bowl, whisk together the oats, brown sugar, baking powder, salt, and cinnamon.
In another medium bowl, whisk together the milk, egg, coconut oil, and maple syrup.
Pour the oat mixture evenly into the baking pan. Pour the milk mixture slowly over the oats. Gently shake the baking dish to make sure the milk covers the oats evenly. It will likely start bubbling - that's a good thing! It's the baking powder, which will make it rise and become cake-like.
Bake for 40 minutes, until the top is golden and oatmeal is set. Let cool for 5 minutes, then serve warm topped with berries, nuts, nut butter, or a drizzle of maple syrup and a splash of milk!
Store any leftovers in the refrigerator for up to a week.
Notes
To prepare breakfasts for the week: after the oatmeal is baked, portion it out among individual containers, top with your favorite toppings, refrigerate, and reheat each morning with a little extra milk!