To prepare bread, lightly spoon flour into dry measuring cups; level with a knife.
Combine flour and next 3 ingredients (through baking soda) in a large bowl, stirring with a whisk; make a well in center of mixture.
Combine granulated sugar and next 4 ingredients (through 1 tablespoon juice).
Add sugar mixture to flour mixture, stirring just until moist. Fold in zucchini and walnuts. Divide batter between 2 (8 x 4inch) loaf pans coated with cooking spray.
Bake at 350 for 50 minutes or until a wooden pick inserted in center comes out clean. Cool 10 minutes in pans on a wire rack; remove from pans.
To prepare glaze, combine powdered sugar and 2 tablespoons juice, stirring with a whisk.
Drizzle evenly over warm loaves. Cool completely on wire rack.