Chop any large pieces of mushroom in the risotto. Drain the mozzarella balls. Press 1 ball into 1 tablespoon risotto and shape to encase the cheese. Repeat to make 12 risotto balls.
Put the flour, eggs and breadcrumbs onto 3 separate large plates. Roll the risotto balls in the flour, then the eggs and finally in the breadcrumbs. Put on a plate and chill for 30 minutes or overnight.
Fill a medium pan with oil to 5cm, then heat until a cube of bread turns golden in 30 seconds. Fry the balls until golden brown, 3 to 4 minutes. Drain well on kitchen paper. Serve hot with lemon wedges to squeeze over and a tomato salsa to dip.