To begin, preheat your oven to 350 and spray a muffin pan with non-stick spray (or line with cupcake liners).
To a large mixing bowl, add your butter and brown sugar and beat together with a mixer till creamy. Add your banana and beat it in. Next, add your milk, vanilla and eggs and mix again briefly till just combined.
To the same bowl, add your flour, cinnamon, nutmeg, baking soda, and salt and stir everything together till you have a smooth muffin batter. Add your zucchini to the batter and gently fold it in.
Fill each muffin tin about 2/3 way full with batter. Bake in the oven for 22-25 minutes, or till the top is springy and a toothpick inserted comes out clean.
Let cool, then devour!
Stored in an airtight container in the fridge, these muffins should last about a week.