Lightly spoon flour into a dry measuring cup; level with a knife. Combine flour, baking powder, and next 4 ingredients in a large bowl; stir well with a whisk.
Combine egg, brown sugar, oil, pumpkin, and buttermilk in a bowl; stir with a whisk until blended. Add pumpkin mixture to flour mixture, and stir until well combined.
Coat a waffle iron with cooking spray; preheat. Spoon about 1/4 cup of batter per waffle onto hot waffle iron, spreading batter to edges. Cook 5 to 7 minutes or until steaming stops; repeat with remaining batter.