Preheat oven to 350F. Coat a 9×13 dish with cooking spray. In a large non-stick pan, saute onions, garlic, celery and green pepper until soft, about 5 minutes. Add kidney beans, broth, chilies, sour cream, salt, cumin, pepper and soup. Bring to a boil, stirring constantly. Remove from heat and stir in shredded chicken. Spread 1/3 of the mixture into the bottom of the dish. Top with half of the tortillas, overlapping and cutting as necessary to fit. Top with 1/3 sauce mixture, then sprinkle on half of the cheese. Cover with remaining tortillas, followed by remaining sauce. Sprinkle remaining cheese over sauce and top with green onions. Bake for 30-35 minutes, until bubbly. Let stand for 10 minutes before slicing for serving.