Heat oven and prepare the pans. Adjust oven rack to the middle position and preheat to 350 degrees F. Grease two 8.5-by 4.5-inch loaf pasn generously with nonstick cooking spray.
Combine the dry ingredients in a large bowl. Whisk together the gluten-free flour, spices, baking soda, baking powder, and salt in a large bowl. Add the brown and granulated sugar. Break up any pieces of brown sugar. You can do this by rubbing the piece of brown sugar between your fingers and thumb or by using a fork.
Mix the batter. Add the pumpkin, eggs, and vegetable oil. Mix until smooth. The batter will be thick.
Bake the loaves. Divide batter evenly between prepared pans. Bake until set and golden brown, about 50 minutes. A cake tester inserted into the center of the loaf should come out clean or to an internal temperature of 206°F.
Cool on a wire rack. Place the pan on a wire rack to cool. Once cool to the touch, turn out onto a wire rack to cool completely.
Store on the counter or freeze. Wrapped tightly in foil, gluten-free pumpkin bread keeps up to 3 days at room temperature. Freeze the cooled loaf, wrapped in plastic wrap and foil, for up to four months.
The Gluten-Free Flour
This recipe was tested with Bob's Red Mill 1:1 Gluten-Free Baking Flour. Using a different flour or blend will affect the bread.