First, preheat the oven to 350F. Line a muffin tin with 12 muffin liners.
In a large bowl, mix together the pumpkin puree, vegetable oil, milk, vanilla, and brown sugar.
Stir in the flour, baking soda, and pumpkin spice mix. Divide the batter evenly among the 12 muffin liners.
Now, prepare the streusel. In a small bowl, mix together the melted coconut oil/vegan butter, brown sugar, and pumpkin spice mix.
Stir in the flour, oatmeal, and pumpkin seeds.
Sprinkle the streusel mixture evenly among the muffins.
Bake for 20-22 minutes, until golden brown and fluffy.
While the muffins bake, make the glaze. In a small bowl, sift the powdered sugar. Add in the vanilla extract and then the milk, a bit at a time, until you reach the right consistency.
When the muffins are ready, top with the glaze and enjoy!