Rinse the chicken thoroughly and be sure to save any fat from the cavity—it will be used for the rice. Place the chicken on a plate and pat it completely dry with paper towels. Rub the exterior with salt to help firm up the skin and give it a pleasant sheen. Set aside.
Fill a large stockpot with 12–14 cups of water and bring it to a boil with the ginger slices and whole scallions. Carefully lower the chicken into the pot, breast-side up. Adjust the water level so the top of the breast just emerges from the surface to prevent overcooking the white meat.
When the water reaches a boil again, lift the chicken to drain any cold water trapped inside the cavity, then gently lower it back into the pot. Bring the water back to a gentle boil once more. As soon as small bubbles begin to rise, reduce the heat to a low simmer. Keep the lid on and maintain a gentle simmer for 30–35 minutes—approximately 10–11 minutes per pound. For larger birds (over 3½ pounds), expect to simmer for 40–50 minutes.
Toward the end of the cooking time, prepare a large ice bath. To test doneness, insert a toothpick into the thickest part of the thigh; if the juices run clear, it's ready. Carefully lift the chicken from the broth, drain the cavity, and lower the bird into the ice bath to stop the cooking process. Let cool for 15 minutes. Drain well and cover with plastic wrap until ready to serve.
You may choose to leave the poaching liquid on a low simmer to intensify its flavor for use in the rice.