Preheat your oven to 375°F (190°C) and line a standard 12-cup muffin tin with paper liners or generously grease with non-stick spray.
In a medium bowl, whisk together the flour, brown sugar, and cinnamon for the streusel. Add the cold, cubed butter and use a pastry cutter or your fingertips to work it into the dry ingredients until the mixture resembles coarse crumbs. Fold in the chopped pecans and set aside.
In a large bowl, whisk together the flour, baking soda, cinnamon, nutmeg, ginger, and salt for the muffin batter.
In a separate bowl, whisk together the pumpkin puree, granulated sugar, brown sugar, eggs, oil, milk, and vanilla extract until smooth and well combined.
Pour the wet ingredients into the dry ingredients and gently fold together using a rubber spatula. Mix just until combined and no dry flour pockets remain – about 12-15 strokes maximum.
Divide the batter evenly among the prepared muffin cups, filling each about ¾ full.
Generously sprinkle the streusel topping over each muffin, gently pressing it into the batter slightly so it adheres during baking.
Bake in the preheated oven for 20-22 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs.
Allow the muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.