Preheat oven to 375˚. Grease a 13x9 baking dish, and line with parchment paper.

In a large bowl, combine sugar, oil, eggs, pumpkin and water. In a separate bowl, mix the gluten-free flour mix, baking powder, baking soda, salt, cloves, nutmeg, and cinnamon. Mix the dry into the wet ingredients until fully combined. Pour the batter into the prepared baking dish, and bake for about 45 minutes, or until center is firm, and a toothpick inserted in the center comes out clean. Let cool for a few minutes in the pan, then holding onto the parchment, carefully lift from pan and transfer to a wire rack to cool completly.

In a medium bowl, cream the butter and brown sugar. Stir in the milk. Add in the powdered sugar a few tablespoons at a time, stirring to incorporate each time before adding the rest.

When the pumpkin bars are cool, use an offset spatula to spread the icing on top in an even layer. Slice into bars and enjoy.