1. Preheat oven to 350°.
2. Weigh or lightly spoon flour into dry measuring cups; level with a knife. Combine flour, salt, and next 4 ingredients (through pumpkin pie spice) in a medium bowl; stir with a whisk.
3. Combine 1/2 cup water and flaxseed.
4. Place sugar and next 4 ingredients (through eggs) in a large bowl; beat with a mixer at medium-high speed until well blended. Add flaxseed mixture and pumpkin; beat at low speed just until blended. Add flour mixture; beat just until combined. Divide batter between 2 (9 x 5–inch) loaf pans coated with cooking spray. Bake at 350° for 1 hour and 10 minutes or until a wooden pick inserted in center comes out clean. Cool 10 minutes in pan on a wire rack; remove from pans. Cool completely on wire rack.