Preheat oven to 375 degrees F (190 degrees C). Spray 21 muffin cups with cooking spray.
Stir cornbread mix, baking powder, and pumpkin pie spice together in a large bowl. Add pumpkin puree and water to cornbread mixture; stir until batter is just-combined. Divide batter between prepared muffin cups.
Bake in the preheated oven until a toothpick inserted into the center of a muffin comes out clean, about 20 minutes.