In a large mixing bowl, combine leftover mashed potatoes, grated cheddar cheese, chopped scallions, parsley, egg, onion powder, and cayenne pepper. Stir well until incorporated. Gradually fold in flour until just combined.

Using a ¼-cup measuring cup, scoop out the mixture and form patties. If too sticky, chill in the fridge for 15 minutes. Coat each in panko breadcrumbs and flatten to about ½-inch thick.

Heat 2 tablespoons of avocado oil in a cast-iron skillet over medium heat. Place patties in the skillet and cook for 2-3 minutes per side until golden brown.

Transfer cooked pancakes to a plate lined with paper towels. Garnish with chopped scallions and serve warm with sour cream.