For crust, mix flour, oatmeal, brown sugar and butter on low speed until crumbly. Press into 9x13 pan. Bake at 350° for 13-15 minutes.
For filling, mix pumpkin, milk, eggs, sugar and spices. Pour into crust. Bake 20 minutes at 350°.
For topping, mix pecans or oatmeal, brown sugar and butter. Crumble over top of hot dessert. Bake 15-20 minutes at 350°. When cool, top with Cool Whip.
NOTE: For a thicker dessert, double the filling ingredients. You would need to bake the filling portion for 30 minutes rather than 20 before putting on the topping.