01 - In a large mixing bowl, combine cold mashed potatoes, shredded cheddar cheese, green onions, garlic powder, black pepper, salt, and 1 egg. Mix thoroughly to achieve an even consistency.
02 - Scoop heaping tablespoons of the mixture and roll each portion into a ball approximately 1 1/4 inches in diameter. Set formed balls aside on a tray.
03 - Arrange three separate shallow bowls: one with flour, one with beaten eggs, and one with breadcrumbs.
04 - Roll each potato ball in flour, dip into the beaten eggs, and then coat evenly with breadcrumbs. Return coated balls to the tray.
05 - Place the tray of breaded potato balls in the refrigerator and chill for at least 20 minutes to firm them up.
06 - Heat vegetable oil in a deep fryer or heavy-bottomed pot to 350°F (175°C).
07 - Working in batches, gently lower the chilled balls into the hot oil. Fry for 2 to 3 minutes per batch, turning occasionally, until uniformly golden and crisp.
08 - Remove fried balls with a slotted spoon and place them on paper towels to drain excess oil. Serve immediately while hot.