Grate zucchini and place it in a colander with several layers or cheesecloth, paper towels, or a clean dish towel. Squeeze to remove excess water.
In a large bowl, whisk together grated zucchini, sugar, melted butter, eggs, sour cream, sourdough discard, and vanilla.
In a separate bowl, whisk together flour, baking soda, baking powder, salt and cinnamon.
Add dry ingredients to wet ingredients, folding gently until only a few streaks of flour remain. Fold in chocolate chips, just until combined.
Optional: Let batter rest for an hour at room temperature. This gives the flour time to absorb the liquid and allows the sourdough flavor to develop slightly.
Preheat oven to 350° F. Line a muffin pan with paper liners.
Scoop batter into prepared muffin tins, filling all the way to the top.
Bake until tops spring back when touched, 15-20 minutes. Allow to cool a few minutes before removing from muffin tin; finish cooling on a wire rack.
Enjoy warm or warm temperature, split and buttered. Delicious!