Prepare the Ingredients. Preheat your oven and grease a 9x9 baking dish. Chop the apple into small pieces and set aside.
Mix the Ingredients. In a large bowl, combine the rolled oats, chopped apple, raisins, cinnamon, baking powder, and salt. In a separate bowl, whisk together the milk, maple syrup, and eggs until well combined.
Combine and Bake. Pour the wet ingredients into the dry ingredients and mix until everything is evenly incorporated. Transfer the mixture to the prepared baking dish and spread it out evenly. Bake in the 350F preheated oven for 35-40 minutes or until the oatmeal is golden brown and set.
Serve Warm. Once baked, remove the oatmeal from the oven and let it cool slightly. Serve warm with a drizzle of maple syrup and a sprinkle of cinnamon for an extra touch of sweetness and flavor.