Preheat oven to 350°; spray 9 ½-inch deep-dish pie plate with cooking spray. Melt butter in large skillet over medium heat. Add celery and onion; cook 5 minutes or until tender, stirring occasionally. Remove from heat; stir in soup, chicken, vegetables, thyme, salt and pepper.
Transfer chicken mixture to prepared plate; top with biscuits and bake 30 minutes or until biscuits are golden brown and cooked through. Makes about 8 cups.