Preheat oven to 350 degrees F. Coat a 24-cup mini muffin tin with cooking spray.
Pulse oats in a blender until finely ground. Add baking powder, cinnamon, baking soda and salt; pulse once or twice to blend. Add zucchini, eggs, brown sugar, oil and vanilla; puree until smooth. (The batter will be wet.) Stir in chocolate chips, if using. Fill the prepared muffin cups.
Bake until a toothpick inserted in the center comes out clean, 15 to 17 minutes. Cool in the pan on a wire rack for 5 minutes, then turn out to cool completely.
