In a bowl, combine flour, sugar, baking soda, cinnamon and salt. Beat the egg, oil, milk, lemon juice and vanilla; stir into dry ingredients just until moistened. Fold in zucchini, chocolate chips and walnuts. Fill 12 greased or paper-lined muffin cups two-thirds full.
Bake at 350° for 20-25 minutes or until a toothpick comes out clean.
Freeze option: Freeze cooled muffins in an airtight container. To use, thaw at room temperature or, if desired, microwave each muffin on high for 20-30 seconds or until heated through.