Preheat oven to 400°F. Grease or paper-line 36 mini muffin cups (or this recipe makes 12 large muffins).
Combine the flour, sugar, baking powder, baking soda, and cinnamon in a mixing bowl.
Beat egg with milk, oil, and lemon juice in a small bowl.
Pour liquid ingredients over the dry. Add zucchini. Mix until just combined.
Spoon batter into muffin tins until they are about 2/3 full.
Bake for 10-12 minutes, or until lightly browned.
Let cool completely and frost with chocolate buttercream.