Preheat your waffle iron to the medium-high setting if that's an option. Spray it with a nonstick spray.
While the waffle iron is heating up, prepare your batter. In a large bowl, mix together the mashed potatoes, oil, egg, buttermilk, bacon, goat's cheese, and spinach until fully combined.
In a separate small bowl, whisk together the flour, baking powder, baking soda, salt, and black pepper. Add the dry ingredients to the wet and stir until just combined.
Add about 1/2 cup of the batter to the center of the waffle iron. It won't be as easy to spread as a typical waffle batter. Very gently smooth it out so that it just covers a portion of each square or triangle of your waffle iron. Close the waffle iron and cook until either your waffle iron says that it's ready or wait about 4-5 minutes if you don't have a timer integrated in your waffle iron.
Be careful pulling the waffle away from the waffle iron, and transfer it to a small plate. Repeat for the rest of the batter.
Serve the waffles immediately. I like them served with sour cream, but they are good all by themselves also! Enjoy!