Preheat broiler. Split turkey tenderloin in half horizontally to make two portions, each about 1/2 inch thick. Place turkey on the unheated rack of a broiler pan. In a small bowl, combine lemon juice, oil, seasoned salt, dried sage, and garlic. Brush mixture on both sides of each turkey portion.
Broil turkey 4 to 5 inches from the heat for 5 minutes. Turn turkey; place lemon slices on turkey. Broil for 2 minutes more. Using a clean brush, brush with apple jelly. Broil for 2 to 3 minutes more or until tender and no longer pink (170 degrees F). Slice the turkey. If desired, garnish with fresh sage leaves.