Line baking sheets with parchment paper or line with lightly greased foil.
Combine the flour, oats, baking soda, baking powder, salt, cinnamon and nutmeg in a medium bowl.
By hand or with a mixer, blend the melted butter, brown sugar and granulated sugar in a large mixing bowl until combined, then add the pumpkin and mix in completely.
Gradually beat in the flour mixture, then stir in the morsels and any other add-ins.
Drop by 2 tablespoons portions (#30 scoop) 2 inches apart onto prepared baking sheets.
Bake for 14 to18 minutes or until light golden brown.
Remove from the oven and leave on the baking sheets for a full 5 minutes; then remove from the parchment and place on a cooling rack..
While cookies cool, sift the confecitoner's sugar into a small bowl, then add the vanilla and 1 tablespoon of water, adding more water, a few drops at a time if necessary, to achieve smoothly flowing icing.
With the cookies still on the cooling rack, slide a large sheet of parchment under the rack.
Scoop the icing into a zip-top sandwich bag then snip off a tiny corner of the bag and drizzle the icing back and forth over the cookies.
Let the icing dry, then store the cookies at room temperature, tightly covered.
Notes
Up to 1 cup of toasted and chopped nuts (pecans, walnuts) or dried fruit (cranberries, raisins, currants) may be added to the dough with the morsels.
Recipe by MJ Bakes A Lot at https://mjbakesalot.com/?p=988