In a large bowl, combine the cooled risotto, mozzarella cheese, Parmesan cheese, garlic powder, oregano, salt, and black pepper. Mix well until all ingredients are evenly incorporated.

Using your hands, take about 2 tablespoons of the risotto mixture and form it into a ball. Repeat with the remaining mixture, placing the formed balls on a baking sheet lined with parchment paper.

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

Roll each risotto ball in the flour, then dip it into the beaten eggs, and finally coat it with breadcrumbs. Make sure each ball is fully covered.

In a large skillet, heat about 1 inch of vegetable oil over medium heat until it reaches 350°F. Carefully add the breaded arancini balls in batches, frying them for about 3-4 minutes on each side or until golden brown.

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.