Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper, or lightly grease it with cooking spray or olive oil.
Combine in a large bowl the chilled mashed potatoes, shredded cheddar cheese, grated Parmesan cheese, eggs, chopped green onions (if using), garlic powder, onion powder, salt, and pepper. Mix until everything is well combined and creamy.
Scoop out portions of the potato mixture using a spoon or your hands, shaping them into small balls or mounds about the size of golf balls.
Roll each puff in breadcrumbs to coat them evenly.
Place the coated potato puffs on the prepared baking sheet, ensuring they are spaced evenly apart.
Bake in the preheated oven for 25–30 minutes, or until the puffs turn golden brown and crispy.
Cool for a few minutes before serving. Enjoy them warm!