Preheat the oven to 350 degrees Fahrenheit (175 degrees Celsius). Grease an 8x8 inch baking dish with cooking spray, or line it with parchment paper.
In a large bowl, stir together the oats, protein powder if using, baking powder, pumpkin pie spice, cinnamon and salt.
2 cups old fashioned rolled oats, ¼ cup vanilla protein powder, 1 teaspoon baking powder, 1 teaspoon pumpkin pie spice, 1 teaspoon ground cinnamon
In a separate medium bowl, whisk the eggs, then whisk in the pumpkin puree, vanilla, maple syrup, milk and melted butter until smooth.
½ teaspoon salt, 1 cup canned pumpkin puree, 2 large eggs, 2 teaspoons vanilla extract, ¼ cup pure maple syrup, ½ cup milk of choice, 1 tablespoon butter
Pour the dry ingredients into the wet ingredients and stir until everything is well combined. Pour the batter into the prepared baking dish.
Bake for 35 to 40 minutes, until a toothpick inserted in the center comes out clean.
Let the baked oatmeal cool completely before adding the glaze. If you are making it ahead, store the glaze separately.