To begin, preheat your oven to 425 and spray a muffin tin with no-stick spray.
To a small mixing bowl, add your flour, cinnamon, nutmeg, baking soda and salt and stir them together.
To a large mixing bowl, add your butter, brown sugar and applesauce and whisk them together till well combined (or beat them lightly with a hand mixer). Add your milk, vanilla and eggs and whisk again till well combined.
Pour your dry ingredients into your wet ingredients and stir together till you have a smooth, even batter. Add your zucchini and apple and gently fold them into your batter. Fill each muffin tin about 3/4 full with the muffin batter.
In a small mixing bowl, add your cinnamon sugar topping ingredients and stir them together. Sprinkle the topping evenly across the tops of your muffins (about 1 overflowing teaspoon of topping for each muffin).
Bake in the oven for 5 minutes, then reduce your oven to 350 and bake for another 17-19 minutes, or till the tops are springy to touch and a toothpick inserted comes out clean.
Stored in an airtight container in the fridge these muffins will last about 5-7 days.