Preheat & Prep. To start, preheat the oven to 350 degrees F. Lightly grease a 9x9 or 2-quart baking dish and set aside.
Combine Dry Ingredients. In a large mixing bowl, combine gluten-free oats, chopped pecans, ground flax, baking powder, cinnamon, nutmeg, and salt. Whisk until evenly blended.
Add Wet Ingredients. Next, add almond milk, applesauce, maple syrup, vanilla, and the diced apples. Stir to combine. (It'll look soupy at this point!)
Bake. Pour the oatmeal mixture into the prepared pan and smooth the surface with a spatula. Bake 30-35 minutes, or until golden brown on top.
Cool & Serve. Let oatmeal cool for 5-10 minutes before slicing and serving. Enjoy warm with a splash of almond milk and a drizzle of pure maple syrup, if desired. Store leftovers covered or in an airtight container in the fridge 2-3 days.