01 - In a large mixing bowl, thoroughly combine the cold mashed potatoes, shredded cheddar cheese, chopped green onions, garlic powder, black pepper, salt, and one egg until uniform.
02 - Portion heaping tablespoons of the mixture and roll into uniform balls approximately 1 1/4 inches in diameter. Arrange on a tray.
03 - Arrange three separate bowls: one containing flour, one with the beaten eggs, and one with breadcrumbs.
04 - Dredge each potato ball first in flour, then coat evenly in beaten egg, and finally roll in breadcrumbs for full coverage.
05 - Place coated balls on a tray and refrigerate for at least 20 minutes to firm up before frying.
06 - Add vegetable oil to a deep fryer or heavy-bottomed pot and heat to 350°F (175°C).
07 - Fry the potato balls in batches for 2 to 3 minutes, turning as needed, until golden brown and crisp.
08 - Lift the fried balls with a slotted spoon and drain briefly on paper towels. Serve hot.