Place the cooked sweet potato, oats, flour, milk, eggs, baking powder, cinnamon, salt, and orange zest into a blender. Blend until well combined and there are no chunks of sweet potato left.
Spray the preheated waffle iron with cooking spray and pour in ⅓ cup batter. Cook until the outsides of the waffles are golden and cooked through, about 6–8 minutes. Serve with maple syrup and chopped pecans, if desired.