Preheat your oven to 350°F (175°C) to ensure even baking.
Grease the muffin tin with oil or line it with muffin liners for easy removal.
In a large mixing bowl, whisk together the gluten-free flour, cinnamon, baking powder, baking soda, salt, and nutmeg until well combined.
In another bowl, mix the maple syrup, avocado oil, applesauce, granulated sugar, eggs, and vanilla extract until smooth.
Finely grate the zucchini; do not squeeze out the liquid as it adds moisture to the muffins.
Pour the wet mixture into the dry ingredients and stir until just combined, being careful not to over-mix.
Gently fold in the grated zucchini, half of the chocolate chips, and the chopped walnuts into the batter.
Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full, and sprinkle the remaining chocolate chips on top. Optionally, add sanding sugar for a sweet crunch.
Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for about 5 minutes before transferring to a wire rack to cool completely. Enjoy warm or at room temperature!
