Rice balls stuffed with tuna

In a saucepan, combine the rinsed rice, salt, and water. Cook over medium heat for 15 minutes, or until the rice is tender and the water is absorbed. Let stand for a few minutes.
Drain the tuna and place it in a bowl. Add the mayonnaise, tomato sauce, chopped parsley, salt, and pepper. Mix well and set aside.
Place the cooked rice in a bowl and add the rice vinegar. Mix well to distribute the flavor and set aside.
Take a piece of plastic wrap and place about 2 tablespoons of rice on top. Press down to flatten it slightly. Add a tablespoon of tuna filling and a cube of mozzarella cheese to the center if desired.