Preheat oven to 350 degrees F and lightly grease an 8x8" baking dish.
Mix all streusel ingredients together in a small bowl until crumbly.
In a medium bowl, whisk together oats, baking powder, pumpkin pie spice, and salt.
In a large bowl, whisk together pumpkin puree, milk, egg, maple syrup or brown sugar, melted butter, and vanilla.
Add the dry ingredients to the wet ingredients and stir until combined.
Pour the mixture into the prepared baking dish and top evenly with the pecan streusel topping.
Bake for 35-40 minutes, until oatmeal is just set and turning golden on top. Let cool for a few minutes before slicing and enjoying.