Preheat oven to 350°.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and the next 7 ingredients (flour through cloves) in a large bowl; make a well in center of mixture. Combine sugar and the next 5 ingredients (sugar through pumpkin) in a bowl, and stir well with a whisk until smooth. Add to flour mixture, stirring just until moist.
Spoon batter into 2 (8 x 4-inch) loaf pans coated with cooking spray, and sprinkle with walnuts. Bake at 350° for 1 hour or until a wooden pick inserted in center comes out clean. Cool loaves in pans 10 minutes on a wire rack; remove from pans. Cool loaves completely; cut each loaf into 12 slices.