To make the pumpkin puree: Cut pumpkin in half with a serrated knife, and clean out seeds and stringy insides. Slice each half into quarters. Place pumpkin slices in a large pot with a steamer basket, and add about 1-inch of water to the pot. Cover, and increase heat until steam begins. Reduce heat to low, and keep pot covered. Steam for about 15-20 minutes, or until pumpkin is soft. Scoop out soft pumpkin with a spoon or scoop. Puree pumpkin with a hand blender until smooth. Cool at room temperature.
Preheat oven to 350 degrees. Coat two 9x5" loaf pans with baking spray.
Stir together sugar, oil, eggs, and pumpkin.
In a separate bowl, whisk together dry ingredients. Mix the pumpkin mixture with the dry, adding 1/2 cup water a little at a time. Pour into prepared pans.
Bake for 45-55 minutes in preheated oven, or until toothpick insert in center comes out clean.