Heat a grill pan over medium-high heat. Sprinkle shrimp with salt and black pepper. Coat pan with cooking spray. Add half of shrimp to pan; cook 2 minutes on each side or until done. Remove shrimp from pan; repeat procedure with remaining shrimp. Cool shrimp for 5 minutes.
Place shrimp in a medium bowl; stir in celery and next 6 ingredients (through cumin). Arrange 2 lettuce leaves on each of 4 plates; top each serving with 3/4 cup shrimp mixture.