Line a 12-cup muffin pan with paper liners. Preheat oven to 400°F.
Combine flour, oats, brown sugar, cinnamon and nutmeg in a mixing bowl. Using two knives, a pastry blender, stand mixture or your fingers, cut in butter until mixture resembles coarse crumbs. Set aside 1/2 cup of this mixture for topping. Stir in baking powder and salt into remaining mixture.
Beat eggs, milk and zucchini in a small bowl. Add to dry ingredients all at once, stirring just until moistened.
Spoon batter into prepared muffin pan. Sprinkle topping evenly over batter; pat down gently.
Bake for 20-25 minutes or until tops spring back when lightly touched.