In a large bowl, blend oats, baking powder, pumpkin pie spice, and salt. In a separate bowl, combine brown sugar, milk, pumpkin, vanilla extract, and eggs, and mix thoroughly.
Combine the wet mixture with the dry mixture until moistened, being careful not to overmix. Gently fold in the pecans, saving a tablespoon for topping. Pour the mixture into the prepared baking dish and sprinkle with the reserved pecans. Bake for 35 to 40 minutes or until it turns golden brown and sets.