Preheat the oven to 350°F. Grease a 12-cup muffin pan with butter and 3 cups of a second muffin pan if you have one - if not you can bake them in 2 batches.
In a large mixing bowl on medium speed beat the oil, eggs, sugar, pumpkin, spices, salt, and baking powder together until smooth about 2 minutes.
Stir in the flour by hand just until smooth - don't overmix or the muffins can become rubbery.
Fill the muffin wells about ¾ full. Bake 22 - 25 minutes or until a toothpick comes out clean from the center.
Cool on a wire rack 15 minutes or so then turn out and cool completely.
In a medium mixing bowl beat the cream cheese and butter together on medium speed 2 minutes.
Beat in 1 teaspoon milk, the cinnamon and vanilla.
Beat in the confectioners' sugar with a teaspoon of milk at a time until it reaches the right consistency. You can make it thin and drizzle or dunk the tops or on the thicker side like an icing. You can also skip the icing and do a cinnamon sugar coating.
Ice the muffins and sprinkle a few nuts on top. Store tightly covered in a cool, dry place up to 4 days.