01 - In a large mixing bowl, thoroughly combine cold mashed potatoes, shredded cheddar cheese, green onions, garlic powder, black pepper, salt, and one large egg until fully incorporated.
02 - Scoop out heaping tablespoons of the mixture and roll each into balls approximately 1 1/4 inches in diameter. Arrange on a tray.
03 - Set up three shallow bowls: one with all-purpose flour, one with beaten eggs, and one with breadcrumbs.
04 - Roll each potato ball in flour, dip in the beaten eggs, then coat evenly with breadcrumbs.
05 - Place all coated balls on a tray and refrigerate for at least 20 minutes to set their shape.
06 - Pour vegetable oil into a deep fryer or heavy-bottomed pot and heat to 350°F (175°C).
07 - Working in batches, fry the potato balls for 2 to 3 minutes per batch, turning occasionally, until golden brown and crispy.
08 - Remove with a slotted spoon and drain on paper towels. Serve immediately while hot.