Preheat your oven to 400°F (200°C) and lightly grease a baking sheet with cooking spray or oil.
In a large bowl, combine the cooled mashed potatoes, cheddar cheese, Parmesan cheese, green onions, egg, garlic powder, onion powder, black pepper, and salt. Mix until well combined.
Using your hands or a spoon, form the potato mixture into small balls or puffs, about 1 to 1.5 inches in diameter.
Roll each puff in breadcrumbs until fully coated, then place them on the prepared baking sheet.
Bake in the preheated oven for 20-25 minutes, or until the puffs are golden brown and crispy on the outside.
Remove from the oven and let cool for a few minutes before serving.