Preheat oven to 350ºF.
Mix non-dairy milk and vinegar or lemon juice together in a small bowl.
Mix flour, baking soda, salt, and cinnamon in a large mixing bowl.
Lightly beat the egg and add it plus the vanilla, oil, and non-dairy milk mixture to the dry ingredients. Mix with a whisk until just fully blended. Do not over mix.
Gently stir in the zucchini, apple, chocolate chips, and walnuts.
Grease or line the individual muffin cups in the muffin tin with parchment paper or cupcake papers.
Pour batter into individual muffin cups in the muffin tin until each cup is ⅔ full.
Bake for 20-25 minutes or until a toothpick can be inserted into the middle of the muffins and come out clean.