Preheat oven to 425°F. Put flour and panko onto two plates and spray a rimmed baking sheet with olive oil.
Roll risotto into 1/4 cup-sized balls. Coat with flour, then egg, and roll in panko until completely coated.
Transfer arancini to baking sheet and spray with additional olive oil, being sure to coat all sides as best as you can. Bake for 25 minutes, or until golden and heated through.