01 - In a large bowl, thoroughly combine cold mashed potatoes, shredded cheddar cheese, green onions, garlic powder, black pepper, salt, and one egg until the mixture is smooth and cohesive.
02 - Portion heaping tablespoons of the potato mixture and shape into balls approximately 1 1/4 inches in diameter. Arrange on a tray.
03 - Set out three separate bowls: one with flour, another with beaten eggs, and the last with breadcrumbs.
04 - Roll each ball first in flour, then dip into beaten egg, and finally coat evenly with breadcrumbs.
05 - Transfer the breaded balls to a tray and refrigerate for a minimum of 20 minutes to firm up.
06 - Heat vegetable oil in a deep fryer or heavy-bottomed pot to 350°F (175°C).
07 - Fry the chilled balls in batches, turning occasionally, until golden brown and crisp, about 2 to 3 minutes per batch.
08 - Remove the fried balls using a slotted spoon and drain on paper towels. Serve immediately while hot.