Preheat oven to 350. Spray a baking dish with nonstick spray or grease with butter. In a large bowl whisk together the pumpkin, egg, milk, and syrup. Set aside. In a smaller bowl, whisk together the oats, spices, brown sugar, and baking powder. Pour the dry ingredients into the wet ingredients and stir to combine. Pour into the baking dish and bake for 20-25 minutes. Remove from oven and brush with melted butter and sprinkle on brown sugar and chopped walnuts. Serve plain or top with extra syrup or whipped cream. Store leftovers in fridge for 2 days.