To make the streusel topping, combine sugars, cinnamon, and salt in a medium bowl. Whisk in melted butter and stir in the flour with a rubber spatula just until moist.
Preheat oven to 425° F. Place paper liners in a regular sized muffin pan.
In a large bowl, whisk together the eggs, brown sugar, granulated sugar, pumpkin and oil until smooth. Add the flour, baking soda, baking powder, pumpkin pie spice and salt and mix until just combined. Fill the paper-lined muffins just over three-fourths of the way full.
Top the batter with the crumb topping until they're overflowing. Push it down slightly to keep it in place.
Bake for 7 minutes at 425 degrees then reduce the heat to 350 and continue to bake for another 10-12 minutes, until a toothpick inserted in the center comes out with a few moist crumbs.
Cool in the muffin pan for 15 minutes then transfer them to a wire rack. While they're cooling, whisk together the powdered sugar and milk. Place a piece of parchment paper under the cooling rack and drizzle the pumpkin muffins with icing.
Store pumpkin streusel muffins in an airtight container at room temperature for up 4 days or in the fridge for up to 1 week. Wrap with plastic wrap and freeze in a freezer bag for up to 3 months. Thaw overnight in the fridge and reheat.