Heat a small nonstick skillet over medium-high heat. Coat pan with cooking spray. Add duck; cook 4 minutes on each side or until a thermometer inserted into thickest portion registers 170°. Cool slightly; coarsely chop duck.
Combine duck, celery, and next 7 ingredients (through wine) in a large bowl. Line each pita half with 1 lettuce leaf; spoon duck mixture evenly into pita halves.