In a large bowl, combine the cooled risotto, mozzarella cheese, Parmesan cheese, garlic powder, oregano, salt, and black pepper. Mix until well combined.

With wet hands, take about 2 tablespoons of the risotto mixture and form it into a ball. Repeat with the remaining mixture to create about 12 balls.

Set up a breading station: Place the flour in one shallow dish, beat the eggs in another dish, and put the breadcrumbs in a third dish.

Roll each risotto ball in the flour, then dip it into the beaten eggs, and finally coat it with breadcrumbs. Ensure each ball is evenly coated.

In a large skillet, heat about 2 inches of vegetable oil over medium heat until it reaches 350°F. Carefully add the arancini balls in batches, frying for about 3-4 minutes or until golden brown and crispy.

Use a slotted spoon to remove the arancini from the oil and place them on a paper towel-lined plate to drain excess oil.

Serve warm with marinara sauce for dipping.