Preheat the oven to 375°F and lightly coat an 8-inch square baking dish with cooking spray.
In a large bowl, stir together the old fashioned rolled oats, baking powder, pumpkin pie spice, cinnamon, and sea salt.
Add the unsweetened almond milk, canned pumpkin, pure maple syrup, ground flaxseed, melted coconut oil, and vanilla. Mix well until combined.
Stir in part of the chopped pecans or walnuts, reserving the rest for the top.
Transfer the mixture to the prepared baking dish and spread it evenly.
Sprinkle the remaining chopped nuts over the top.
Bake for 30 to 35 minutes, until the center is set and the top is lightly golden.
Rest for 5 to 10 minutes before serving. Drizzle with more maple syrup if desired.