Put the rice into a large bowl.
Add 1 egg first and start to mix it with the rice. If the mix looks too dry, then you can add the second egg or just the yolk. What you need is a mix from which you can easily make balls (not too dry, not too loose).
Stir until all the egg coats the rice.
Now, add the Parmesan cheese and stir thoroughly. At this stage, you are free to add other ingredients if you like (i.e.: ham cut into small pieces - but of course the dish is no longer vegetarian!)
Take some of the rice in one hand and put 1 or 2 small mozzarella dices into it. Close the mozzarella inside making a rice ball.
Then, roll the ball in the breadcrumbs.
Flatten the ball, making sure it does not break and that you cannot see any part of mozzarella. The diameter of the disc should be about 4 cm (1 1/2").
This is what you should have before the deep frying stage.
Heat the sunflower oil and when the oil is hot, put the croquettes into the frying pan.
After few seconds move the croquettes gently with a spoon to ensure that they do not stick to the bottom of the pan.
Continue frying for few minutes until the croquettes are golden brown. When ready, remove them from the frying pan and put them into a large dish or bowl lined with some kitchen paper to absorb the excess oil.
This is the final presentation, where all the croquettes are perfectly cooked.