For glaze, heat apple jelly, lemon peel, thyme, ginger, and soy sauce in a small saucepan just until jelly is melted. Reserve 1/4 cup glaze.
Place chicken on the unheated rack of a broiler pan. Broil 5 to 6 inches from the heat for 10 to 12 minutes or until chicken is tender and no longer pink, turning once and brushing with glaze. Or, grill chicken on the rack of an uncovered grill directly over medium coals for 6 minutes. Brush with glaze. Turn; brush with glaze and continue grilling 6 to 9 minutes more or until chicken is tender and no longer pink.
Meanwhile, lightly coat a large saucepan or Dutch oven with cooking spray. Heat over medium heat. Add garlic, leek, and apple; cook 3 minutes. Add the reserved 1/4 cup glaze and cider or broth; heat to boiling. Add spinach; toss just until wilted. Season to taste with salt and pepper.
To serve, slice chicken crosswise into six to eight pieces. Divide greens mixture among four dinner plates. Top with sliced chicken. Makes 4 servings.