Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9x5 inch loaf pan.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, mixing well after each one. Combine the flour, baking soda, salt, 1 teaspoon of cinnamon, 1/2 teaspoon of nutmeg, and ginger. Stir the dry ingredients into the sugar mixture alternately with the pumpkin puree, beginning and ending with the dry ingredients. Fold in the chocolate chips and 3/4 cup of the walnuts until evenly distributed. Spoon into the prepared loaf pan, and sprinkle the remaining walnuts over the top.
Bake for 65 minutes in the preheated oven, or until a knife inserted into the crown of the loaf comes out clean. Cool, then remove from the pan, and drizzle with icing.
To make the icing, stir together the confectioners' sugar and heavy cream with a pinch of cinnamon and nutmeg until smooth.