Preheat oven to 375°F. Line a 12-cup muffin pan and lightly mist with spray.
Whisk flour, baking powder, baking soda, salt, cinnamon, and nutmeg in a bowl.
In a second bowl, whisk pumpkin, both sugars, oil, eggs, milk, and vanilla until smooth.
Add dry mix to wet. Stir gently just until no dry spots remain.
Fold in chocolate chips without overmixing the batter.
Divide batter among cups, filling each about three-quarters full.
Bake 18–21 minutes, until tops spring back and a toothpick comes out clean.
Cool in pan 5 minutes, then transfer muffins to a rack to finish cooling.