Preheat the waffle maker.
In a large bowl, mix the flour, baking powder, cinnamon, and salt.
In another bowl, whisk together the mashed sweet potatoes, milk, eggs, and melted butter until smooth.
Combine the wet and dry ingredients, stirring until just mixed.
Spray the waffle maker with cooking spray.
Pour about 1/3 cup of batter into the waffle maker, spreading it evenly.
Close the lid and cook according to the manufacturer's instructions, usually 5-7 minutes.
Carefully remove the waffle, reapply cooking spray if needed, and repeat with the remaining batter.
Serve warm with syrup or toppings of choice.