Preheat an oven to 350 degrees. Butter and flour a 10” tube pan. In a small bowl, combine flour, cinnamon, baking powder, baking soda and salt. Set aside.
In the bowl of a mixer, combine oil, eggs and pumpkin and ,sugar. Beat until smooth, about 30 seconds. Slowly add the dry mixture into the wet. Once the mixture has come together, turn the mixer up to a medium high speed and beat for 2 minutes. The batter should be light and smooth. Fold walnuts into the batter by hand.
Pour into the prepared pan and bake for 50-60 minutes, or until a toothpick inserted into the cake comes out clean. Cool on a wire rack inside the pan for at least 1 hour. Remove from pan and cool completely.
To make the frosting, whip the cream cheese on high for 1 minute until fluffy. Add vanilla and slowly stir in the confectioner’s sugar. Add milk 1 tablespoon at a time until it reaches the right consistency. The icing should not be thick, but pourable. Whip the frosting on high for another 45 seconds. Pour the icing over the cooled cake using a knife to smooth the outside edges.