Preheat oven to 400 degrees F. Line a 12-cup standard muffin tin with paper liners; set aside.
To make the crumb topping, combine Kit Kat crumbs, brown sugar, butter and cinnamon; set aside.
In a large bowl, combine flour, sugar, cinnamon, nutmeg, baking powder, baking soda and salt. In a large glass measuring cup or another bowl, whisk together bananas, milk, oil and egg. Pour mixture over dry ingredients and stir using a rubber spatula just until moist. Add Kit Kat bars and gently toss to combine.
Scoop the batter evenly into the muffin tray. Top each muffin with 1 teaspoon crumb topping, swirling into the batter using figure eight motions.
Place into oven and bake for 15-17 minutes, or until a tester inserted in the center comes out clean.