Spread a thin layer of seasoned rice onto a bamboo mat lined with plastic wrap. Brush sesame oil on the top of the rice. Add your chosen fillings in a row horizontally across the rice, leaving a small space at the top and bottom. Tightly roll up the mat, using the plastic wrap to help form a compact roll. Seal the seam with a little water. Cut the roll into bite-sized pieces with a sharp knife dipped in water to prevent sticking. Serve kimbap with soy sauce, sesame oil, or pickled ginger.