Preheat the oven to 350°F (175°C), line a 12-cup muffin pan, and lightly squeeze the grated zucchini so it remains moist but not watery.
Combine the oats, whole-wheat flour, baking powder, baking soda, and cinnamon in a large mixing bowl.
In another bowl, whisk the eggs, mashed banana, honey, and milk until smooth and evenly blended.
Stir the zucchini into the wet ingredients, then pour the mixture into the bowl containing the dry ingredients.
Fold gently until just combined, then let the batter stand for about 5 minutes so the oats can begin absorbing moisture.
Divide the batter among the muffin cups and bake for 18–20 minutes until the centers spring back lightly when touched.
Cool for several minutes in the pan before moving the muffins to a wire rack, then store once completely cooled.