Preparation - Grease and flour a 13" x 9" x 2" baking pan; set aside. Combine the cake mix, brown sugar, pumpkin, vegetable oil, eggs, spice, and nuts in a large mixing bowl. Mix on low speed for about 1 minute, or just until the dry ingredients are moistened, then mix at medium speed for about 2 minutes. Spread the batter in the prepared baking pan. In a separate bowl, with a fork, mix the flour, sugar, butter, and cinnamon together until crumbly. Sprinkle the mixture evenly over the cake batter. Bake at 350° for 40 to 45 minutes, or until the cake springs back when touched lightly in the center.