Preheat oven to 450 degrees F if you have no convection fan, or to 425 degrees F if you have a convection fan.
Rinse the chickens inside and out and dry well.
Make the salt: In a bowl, combine the lemon zest, rosemary, salt, and pepper, mixing well. Rub the chicken all over with the olive oil, and then rub with 3 tablespoons of the seasoned salt. (Reserve the remaining salt for another use.) Tuck the rosemary sprigs and lemon chunks into the chicken cavity. You don't need to truss the chicken.
Place the bird on a rack in a roasting pan and roast for 15 minutes. Reduce the oven temperature by 75 degrees F and continue roasting until the juices run clear when a thigh is pierced with a skewer, about 50 to 55 minutes longer. Transfer the chicken to a platter and let rest for at least 10 minutes before carving.