Preheat oven to 350°F. Combine sour cream and enchilada sauce. Set aside.
Cook onion in oil 4 minutes or until slightly tender. Add bell pepper and cook 3 minutes more.
Stir in taco seasoning, chicken and black beans with ⅔ cup water. Bring to a boil, reduce heat and simmer 5 minutes or until thickened.
Place ½ cup enchilada sauce in the bottom of a 9x13 casserole dish. Layer 6 tortillas on top. Add ½ of the chicken mixture and ½ of the cheese. Top with half of the remaining enchilada sauce.
Add 6 more tortillas, remaining chicken mixture, remaining enchilada sauce and finally the remaining cheese.
Bake uncovered 25-30 minutes or until hot and bubbly.