Preheat oven to 350°.
Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 4 ingredients (through baking soda) in a large bowl.
Combine egg substitute and next 4 ingredients (through egg) in a large bowl; add sugar, stirring until combined. Add zucchini; stir until well combined. Add flour mixture; stir just until combined. Stir in walnuts.
Divide batter evenly between 2 (8 x 4-inch) loaf pans coated with cooking spray. Bake at 350° for 1 hour or until a wooden pick inserted in center comes out clean. Cool 10 minutes in pans on a wire rack; remove from pans. Cool completely on wire rack.