To make rice mixture: In a medium bowl, mix together the rice, eggs, Romano cheese, prosciutto, salt, oregano and pepper.
2. To make meat mixture: In a medium saucepan, sauté the onions for 2 minutes.
Add ground beef and cook until browned.
Add tomatoes and simmer for 20 minutes, remove from heat, and set aside to cool.
3. To assemble rice balls: Place 2 tablespoons of the rice mixture in your hand and insert a cube of mozzarella and a teaspoon of the meat mixture into the center.
Roll into a ball and repeat to form the remaining rice balls.
4. To cook rice balls: In a small bowl, beat 1 egg to form an egg wash.
Dip each rice ball in the egg wash and then roll in the bread crumbs.
Heat about 1 1/2 inches of oil to 325°F in an 8- or 10-inch skillet.
Fry the rice balls about 2 minutes on each side, or until golden brown.