Mix the cold mashed potatoes, Parmesan, one beaten egg, garlic powder, onion powder, and black pepper in a bowl.
Form two tablespoons of the potato mixture around a cube of mozzarella, rolling it into a tightly sealed ball.
Bread each ball by rolling it in flour, dipping it in the two beaten eggs, and finally coating it in Panko breadcrumbs.
Heat the vegetable oil to 350 degrees Fahrenheit in a deep skillet or pot.
Fry the breaded balls in small batches for 3 to 4 minutes until golden brown, then drain on paper towels.
