Place the potatoes in steamer basket set over boiling water. Cover and steam until the potatoes are tender, about 10 minutes. Set aside.
Preheat the grill to medium-high. Lightly coat the chicken with cooking spray. Sprinkle with 1/4 tsp. salt. Grill the chicken until cooked through, about 3 minutes per side. Remove from the grill and slice into strips.
In a large bowl combine the potatoes, chicken, green beans, basil, scallions, mayonnaise, lemon zest, 1 Tbs. lemon juice and 1/4 tsp. salt. Stir to combine.
Wash, trim, and cook green beans in boiling water for 5 minutes. Store in the refrigerator until needed.