In a medium mixing bowl, stir together the flour, old fashioned oats, baking powder, pumpkin pie spice, and salt.
1 ¾ cups all-purpose flour, 1 cup old fashioned oats, 2 teaspoons baking powder, 2 teaspoons pumpkin pie spice, ½ teaspoon kosher salt
In a second large bowl, whisk together the pumpkin puree, brown sugar, vegetable oil, milk, eggs, and vanilla extract until smooth.
1 cup 100% pumpkin puree, 1 cup light brown sugar, ½ cup vegetable oil, ½ cup whole milk, 2 large eggs, 1 teaspoon pure vanilla extract
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix.
Divide the batter evenly between the prepared muffin cavities, filling each one about ¾ of the way full. We recommend using a cookie scoop (ice cream scoop size) to make this easy and less messy.
Sprinkle the streusel topping evenly over the muffin batter of each muffin.
Bake the muffins for 18-22 minutes, or until a toothpick inserted into the center comes out clean.
Remove the muffins from the oven and allow them to cool in the muffin pan for about 5 minutes. Then transfer them to a wire rack to fully cool.