Step 1: Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners or grease well with spray.
Step 2: In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt until well combined.
Step 3: In a large bowl, beat the oil and sugar together. Add the egg and vanilla extract, mixing until smooth.
Step 4: Stir the sourdough discard into the wet mixture until fully incorporated.
Step 5: Fold in the grated zucchini. The mixture will look very thick and vegetable-heavy at this point.
Step 6: Gradually add the dry ingredients to the wet ingredients. Fold gently with a spatula just until the flour streaks disappear.
Step 7: Fold in 3/4 cup of the chocolate chips. Reserve the rest for the top.
Step 8: Divide the batter evenly among the muffin cups. Sprinkle the remaining chocolate chips on top of each.
Step 9: Bake for 20-22 minutes, or until a toothpick inserted into the center comes out clean (minus any melted chocolate).
Step 10: Allow the muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.