Mix yogurt, onion and mint in small bowl. Cover. Refrigerate until ready to serve. Mix cumin, garlic powder, pepper and salt until well blended. Sprinkle on chicken tenders.
Grill over medium-high heat 4 to 5 minutes per side or until chicken is cooked through. Toast naan on the grill about 30 seconds. Cut each naan in half and trim as necessary.
Serve chicken on naan topped with lettuce, tomato and cucumber. Serve with yogurt mixture.