In a large bowl, combine the cooked rice, sesame oil, soy sauce, and salt. Mix well until the rice is evenly coated.
Add the black and white sesame seeds, green onions, and your choice of protein and vegetables. 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 using nori, wrap a strip around each rice ball for added flavor and texture.
Place the rice balls on a plate and let them sit for about 10 minutes to firm up before serving.