From the cake mix package reserve 1 cup aside for the topping. Mix the rest of the cake mix with the melted margarine and egg. Combine and press firmly into a greased 9x13-inch pan. Prick with a fork and bake in oven till lightly brown.
Mix pumpkin, milk, pumpkin pie spice, 2 eggs, brown sugar. Combine filling ingredients and pour over crust.
Mix the one cup of reserved cake mix, cinnamon, sugar, and margarine together using a fork till crumbly. Sprinkle over filling.
Bake at 350°F for 40-45 minutes. Serve with ice cream or whipped cream. This has a better flavor the next day.