1. Preheat grill to medium-high heat.
2. Brush both sides of chicken evenly with oil; sprinkle with salt and pepper. Place chicken on a grill rack coated with cooking spray; grill 6 minutes on each side or until done. Let stand 10 minutes; shred. Place chicken in a large bowl. Add celery and next 3 ingredients (through green onions); toss.
3. Combine sour cream and remaining ingredients, stirring well. Add sour cream mixture to chicken mixture; toss to coat.