Preheat your oven to 375°F (190°C). Grease an 8x8 inch baking dish.
In a large bowl, whisk together the rolled oats, baking powder, ½ teaspoon cinnamon, and salt.
In a separate bowl, whisk together the egg, milk, maple syrup, 2 tablespoons melted butter, and vanilla extract.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
Pour half of the oatmeal mixture into the prepared baking dish.
In a small bowl, mix together the 1 tablespoon melted butter, brown sugar, and ½ teaspoon cinnamon for the swirl.
Sprinkle half of the cinnamon-sugar mixture over the oatmeal in the dish.
Pour the remaining oatmeal mixture over the cinnamon-sugar layer.
Sprinkle the rest of the cinnamon-sugar mixture on top.
Bake for 25-30 minutes, or until set and lightly golden brown.
Let cool slightly before cutting into squares.