In a large bowl, combine the cooled rice, drained tuna, mayonnaise, soy sauce, sesame oil, green onions, shredded carrots, salt, and pepper. Mix well until all ingredients are evenly incorporated.
Wet your hands with water to prevent sticking. Take about 2 tablespoons of the mixture and form it into a ball. Repeat until all the mixture is shaped into balls.
Roll each rice ball in panko breadcrumbs for added crunch, if desired.
If using nori, wrap a strip around each rice ball for extra flavor and presentation.
Serve immediately or refrigerate for up to 1 hour before serving to allow flavors to meld.