Cook rice according to package directions. Cool slightly. Stir in the egg yolk, cheese and butter. Cover and refrigerate until cooled.
Meanwhile, in a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Stir in the tomato sauce, peas, salt and pepper.
Shape rice mixture into 11 patties. Place one heaping tablespoonful of meat filling in the center of each patty. Shape rice around filling, forming a ball.
Place egg whites and bread crumbs in separate shallow bowls. Dip rice balls in egg whites, then roll in bread crumbs. In an electric skillet or deep-fat fryer, heat oil to 375°. Fry rice balls, a few at a time, for 1-2 minutes on each side or until golden brown. Drain on paper towels.