Preheat oven to 350°F (175°C) and grease a 9×9-inch pan.
Mix the flour, sugar, baking powder, salt, and pumpkin pie spice in a bowl.
Add pumpkin, oil, vanilla, and milk. Stir until well combined.
Pour batter into the pan.
In a separate bowl, mix the melted butter, flour, brown sugar, cinnamon, and salt for the streusel. Sprinkle over the batter.
Bake for 30-40 minutes or until a toothpick comes out clean.
Let it cool before serving.