In a large bowl, combine the cooked rice, sesame oil, soy sauce, salt, and black pepper. Mix well until the rice is evenly coated.
Add the chopped green onions, shredded carrots, and tofu or ground meat (if using) to the rice mixture. Stir until all ingredients are well incorporated.
Wet your hands with water to prevent sticking. Take a small handful of the rice mixture and shape it into a ball or triangle, about the size of a golf ball.
If desired, wrap the rice ball with a strip of nori for added flavor and presentation.
Repeat the process until all the rice mixture is shaped into balls.
Serve immediately or refrigerate for up to 2 hours before serving. Enjoy as a snack or part of a meal.