To clean the chicken, rub all over with a handful of kosher salt, getting rid of any loose skin. Rinse the chicken well inside and out. Pat dry with paper towels.
Season the chicken generously with salt. Stuff the chicken cavity with the ginger slices and scallions.
Place the chicken in a large stock pot, cover with cold water by 2 cm, and season with salt to taste.
Bring to a boil over high heat, then immediately reduce the heat to low to maintain a simmer. Cover and cook for about 30 minutes, or until the internal temperature of the chicken reaches 165°F (75°C). Remove the pot from the heat.
Remove the chicken from the pot, reserving the poaching liquid for later, and transfer to an ice bath for 5 minutes to stop the cooking process and to keep the chicken skin springy. Discard the ginger and green onion.
After it’s cooled, pat the chicken dry with paper towels and rub all over with sesame oil. This will help prevent the chicken from drying out.