Preheat oven to 350 degrees. Coat a 9 x 5-inch loaf pan with nonstick cooking spray. Gently spoon flour into measuring cups (do not pack). Add flour to a large bowl, followed by the sugar, baking powder, baking soda, salt and nutmeg. Stir well with a wire whisk. In another bowl, combine the zucchini, oil, egg and egg white, vanilla, lemon zest and yogurt. Add zucchini mixture to flour mix, combining until just moist. Pour into loaf pan and bake for 55 minutes to an hour, or until a toothpick inserted in the middle