Preheat oven to 400 ℉. Line muffin pan with liners. Set aside.
FOR THE MUFFINS: In large bowl add butter, milk, eggs, pumpkin, vanilla and brown sugar. Whisk together until completely incorporated.
Add in flour, oats, baking soda and pumpkin pie spice. Stir until combined.
Scoop into muffin liners. Set aside.
FOR THE TOPPING: In small bowl add butter, flour, sugar, oats and cinnamon. Stir together.
Sprinkle the top of each muffin with a little of the topping mixture.
Bake for 12-15 minutes. Cool.
FOR THE DRIZZLE: Whisk together powdered sugar and milk.
Drizzle over muffins.
Serve and ENJOY!