Preheat oven to 350 degrees F.
Using your hands (or mixer), combine flour, oats, brown sugar, and butter until crumbly; press into the bottom of a 13x9 inch baking dish. Bake for 15 mins.
Combine and beat well the following: pumpkin, evaporated milk, eggs, sugar, salt, nutmeg (or ginger), cinnamon, and cloves. Pour over hot crust, and return to oven for an additional 20 minutes.
With your hands, combine nuts, brown sugar and softened butter. Sprinkle over filling and return to the oven for an additional 15 to 20 minutes or until set.
Cool in pan, and cut into bars or squares. Serve with whipped cream or Cool Whip.