Add the cooked rice, garlic, Parmesan, flour, cornflour, salt, pepper, oregano, chili flakes, and melted butter to a large bowl. Mix everything together using your hands.
Take a portion of the mixture about the size of a table tennis ball. Flatten it slightly, place a cube of mozzarella in the center, and press the rice mixture around it to cover the cheese. Roll it between your palms until you have a smooth ball.
Prepare the slurry: Mix the flour, cornflour, and enough water to make a smooth slurry.
Prepare the coating: Mix the panko breadcrumbs and grated Parmesan in a bowl.
Dip each rice ball in the slurry. Then immediately roll it in the panko and Parmesan mixture until evenly covered.
Chill the coated rice balls for 15 minutes before frying.
Heat oil in a deep fryer. Carefully drop the rice balls in hot oil and fry for 5–6 minutes. Turn them occasionally, until golden and crispy. Try not to overcrowd the pan. Fry in batches, if needed.
Transfer the fried balls to a paper towel-lined plate to drain.
