Preheat your oven to 375°F and lightly coat an 8-inch square baking dish with cooking spray.
In a large mixing bowl, combine the oats, baking powder, pumpkin pie spice, cinnamon, and salt. Stir until evenly distributed.
Add the almond milk, canned pumpkin, pure maple syrup, ground flaxseed, melted coconut oil, and vanilla extract to the dry ingredients. Stir well until the mixture is fully combined. Gently fold in 1/4 cup of the chopped nuts.
Pour the oatmeal mixture into the prepared baking dish, spreading it evenly. Sprinkle the remaining chopped nuts on top for added texture and flavor.
Bake for 30-35 minutes, or until the center is set and the top is golden brown. Remove from the oven and let it cool for a few minutes before serving.
Portion into bowls and, if desired, drizzle with additional maple syrup for extra sweetness.